Editing MPEP 2138

<noinclude>{{MPEP Section|2137|2100|2141}}</noinclude>

==[[MPEP 2138|2138 35 U.S.C. 102(g)]]==

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35 U.S.C. 102. Conditions for patentability; novelty and 
loss of right to patent.

A person shall be entitled to a patent unless -

(g)(1) during the course of an interference conducted under 
section 135 or section 291, another inventor involved therein 
establishes, to the extent permitted in section 104, that before such 
person’s invention thereof the invention was made by such other 
inventor and not abandoned, suppressed, or concealed, or (2) 
before such person’s invention thereof, the invention was made in 
this country by another inventor who had not abandoned, suppressed, 
or concealed it. In determining priority of invention 
under this subsection, there shall be considered not only the 
respective dates of conception and reduction to practice of the 
invention, but also the reasonable diligence of one who was first 
to conceive and last to reduce to practice, from a time prior to conception 
by the other.

35 U.S.C. 102(g) issues such as conception, reduction 
to practice and diligence, while more commonly 
applied to interference matters, also arise in other contexts. 

35 U.S.C. 102(g) may form the basis for an ex parte 
rejection if: (1) the subject matter at issue has been 
actually reduced to practice by another before the 
applicant’s invention; and (2) there has been no abandonment, 
suppression or concealment. See, e.g., 
Amgen, Inc. v. Chugai Pharmaceutical Co., 927 F.2d 
1200, 1205, 18 USPQ2d 1016, 1020 (Fed. Cir. 1991); 
New Idea Farm Equipment Corp. v. Sperry Corp., 916 
F.2d 1561, 1566, 16 USPQ2d 1424, 1428 (Fed. Cir. 
1990); E.I. DuPont de Nemours & Co. v. Phillips 
Petroleum Co., 849 F.2d 1430, 1434, 7 USPQ2d 1129, 
1132 (Fed. Cir. 1988); Kimberly-Clark v. Johnson & 
Johnson, 745 F.2d 1437, 1444-46, 223 USPQ 603, 
606-08 (Fed. Cir. 1984). To qualify as prior art under 
35 
U.S.C. 102(g), however, there must be evidence 
that the subject matter was actually reduced to practice, 
in that conception alone is not sufficient. See 
Kimberly-Clark, 745 F.2d at 1445, 223 USPQ at 607. 
While the filing of an application for patent is a constructive 
reduction to practice, the filing of an application 
does not in itself provide the evidence necessary 
to show an actual reduction to practice of any of the 
subject matter disclosed in the application as is necessary 
to provide the basis for an ex parte rejection 
under 35 U.S.C. 102(g). Thus, absent evidence showing 
an actual reduction to practice (which is generally 
not available during ex parte examination), the disclosure 
of a United States patent application publication 
or patent falls under 35 U.S.C. 102(e) and not under 
35 U.S.C. 102(g). Cf. In re Zletz, 893 F.2d 319, 323, 
13 USPQ2d 1320, 1323 (Fed. Cir. 1990) (the disclosure 
in a reference United States patent does not fall 
under 35 U.S.C. 102(g) but under 35 U.S.C. 102(e)).

In addition, subject matter qualifying as prior art 
only under 35 U.S.C. 102(g) may also be the basis for 
an ex parte rejection under 35 
U.S.C. 103. See In re 
Bass, 474 F.2d 1276, 1283, 177 USPQ 178, 183 
(CCPA 1973) (in an unsuccessful attempt to utilize a 
37 CFR 1.131 affidavit relating to a combination 
application, applicants admitted that the subcombination 
screen of a copending application which issued as 
a patent was earlier conceived than the combination). 
35 
U.S.C. 103(c), however, states that subsection (g) 
of 35 U.S.C. 102 will not preclude patentability where 
subject matter developed by another person, that 
would otherwise qualify under 35 U.S.C. 102(g), and 
the claimed invention of an application under examination 
were owned by the same person, subject to 
an obligation of assignment to the same person, or 
involved in a joint research agreement, which meets 
the requirements of 35 U.S.C. 103(c)(2) and (c)(3),
at the time the invention was made. See MPEP 
§ 706.02(l) and § 2146.

For additional examples of 35 U.S.C. 102(g) issues 
such as conception, reduction to practice and diligence 
outside the context of interference matters, see 
In re Costello, 717 F.2d 1346, 219 USPQ 389 (Fed. 
Cir. 1983) (discussing the concepts of conception and 
constructive reduction to practice in the context of a 
declaration under 37 CFR 1.131), and Kawai v. 
Metlesics, 480 F.2d 880, 178 USPQ 158 (CCPA 1973) 
(holding constructive reduction to practice for priority 
under 35 U.S.C. 119 requires meeting the requirements 
of 35 U.S.C. 101 and 35 U.S.C. 112).

2138.01Interference Practice [R-3]

I. 35 U.S.C. 102(g) IS THE BASIS OF 
INTERFERENCE PRACTICE

Subsection (g) of 35 U.S.C. 102 is the basis of 
interference practice for determining priority of 
invention between two parties. See Bigham v. Godtfredsen, 
857 F.2d 1415, 1416, 8 USPQ2d 1266, 1267 
(Fed. Cir. 1988), 35 U.S.C. 135, 37 CFR Part 41, 
Subparts D and E and MPEP Chapter 2300. An 
interference is an inter partes proceeding directed at 
determining the first to invent as among the parties to 
the proceeding, involving two or more pending applications 
naming different inventors or one or more 
pending applications and one or more unexpired patents 
naming different inventors. The United States 
is unusual in having a first to invent rather than a first 
to file system. Paulik v. Rizkalla, 760 F.2d 1270, 
1272, 226 USPQ 224, 225 (Fed. Cir. 1985) (reviews 
the legislative history of the subsection in a concurring 
opinion by Judge Rich). The first of many to 
reduce an invention to practice around the same time 
will be the sole party to obtain a patent, Radio Corp. 
of America v. Radio Eng’g Labs., Inc., 293 U.S. 1, 2, 
21 USPQ 353, 353-4 (1934), unless another was the 
first to conceive and couple a later-in-time reduction 
to practice with diligence from a time just prior to 
when the second conceiver entered the field to the 
first conceiver’s reduction to practice. Hull v. Davenport, 
90 F.2d 103, 105, 33 USPQ 506, 508 (CCPA 
1937). See the priority time charts below illustrating 
this point. Upon conclusion of an interference, subject 
matter claimed by the losing party that was the basis 
of the interference is rejected under 35 U.S.C. 102(g), 
unless the acts showing prior invention were not in 
this country.

It is noted that 35 U.S.C. 101 requires that whoever 
invents or discovers is the party who may obtain a 
patent for the particular invention or discovery. 
35 
U.S.C. 111 (applicant) or 35 U.S.C. 116 (applicants) 
set forth the requirement that the actual inventor(
s) be the party who applies for a patent or that a 
patent be applied for on behalf of the inventor. Where 
it can be shown that an applicant has “derived” an 
invention from another, a rejection under 35 
U.S.C. 
102(f) is proper. Ex parte Kusko, 215 USPQ 972, 974 
(Bd. App. 1981) (“most, if not all, determinations 
under Section 102(f) involve the question of whether 
one party derived an invention from another”); Price 
v. Symsek, 988 F.2d 1187, 1190, 26 USPQ2d 1031, 
1033 
(Fed. Cir. 1993) (Although derivation and priority 
of invention both focus on inventorship, derivation 
addresses originality, i.e., who invented the subject 
matter, whereas priority focuses on which party 
invented the subject matter first.). 



II. PRIORITY TIME CHARTS

The following priority time charts illustrate the 
award of invention priority in several situations. The 
time charts apply to interference proceedings and are 
also applicable to declarations or affidavits filed 
under 
37 CFR 1.131 to antedate references which are 
available as prior art under 35 
U.S.C. 102(a) or 
102(e). Note, however, in the context of 37 CFR 
1.131, an applicant does not have to show that the 
invention was not abandoned, suppressed, or concealed 
from the time of an actual reduction to practice 
to a constructive reduction to practice because the 
length of time taken to file a patent application after 
an actual reduction to practice is generally of no consequence 
except in an interference proceeding. Paulik 
v. Rizkalla, 760 
F.2d 1270, 226 USPQ 224 (Fed. Cir. 
1985). See the discussion of abandonment, suppression, 
and concealment in MPEP § 2138.03.

For purposes of analysis under 37 CFR 1.131, the 
conception and reduction to practice of the reference 
to be antedated are both considered to be on the effective 
filing date of domestic patent or foreign patent or 
the date of printed publication.

In the charts, C = conception, R = reduction to 
practice (either actual or constructive), Ra = actual 
reduction to practice, Rc = constructive reduction to 
practice, and TD = commencement of diligence.

Example 1

Example 1


A is awarded priority in an interference, or antedates 
B as a reference in the context of a declaration 
or affidavit filed under 37 CFR 1.131, because 
A conceived the invention before B and constructively 
reduced the invention to practice before B 
reduced the invention to practice. The same result 
would be reached if the conception date was the 
same for both inventors A and B. 

Example 2

Example 2


A is awarded priority in an interference, or antedates 
B as a reference in the context of a declaration 
or affidavit filed under 37 CFR 1.131, if A can 
show reasonable diligence from TD (a point just 
prior to B’s conception) until Rc because A conceived 
the invention before B, and diligently constructively 
reduced the invention to practice even 
though this was after B reduced the invention to 
practice.

Example 3

Example 3


A is awarded priority in an interference in the 
absence of abandonment, suppression, or concealment 
from Ra to Rc, because A conceived the 
invention before B, actually reduced the invention 
to practice before B reduced the invention to practice, 
and did not abandon, suppress, or conceal the 
invention after actually reducing the invention to 
practice and before constructively reducing the 
invention to practice.

A antedates B as a reference in the context of a 
declaration or affidavit filed under 37 CFR 1.131because A conceived the invention before B and 
actually reduced the invention to practice before B 
reduced the invention to practice.

Example 4

Example 4


A is awarded priority in an interference if A can 
show reasonable diligence from TD (a point just 
prior to B’s conception) until Ra in the absence of 
abandonment, suppression, or concealment from 
Ra to Rc, because A conceived the invention 
before B, diligently actually reduced the invention 
to practice (after B reduced the invention to practice), 
and did not abandon, suppress, or conceal the 
invention after actually reducing the invention to 




 

practice and before constructively reducing the 
invention to practice.

A antedates B as a reference in the context of a 
declaration or affidavit filed under 37 CFR 1.131because A conceived the invention before B, and 
diligently actually reduced the invention to practice, 
even though this was after B reduced the 
invention to practice.



III. 37 CFR 1.131 DOES NOT APPLY IN 
INTERFERENCE PROCEEDINGS

Interference practice operates to the exclusion of ex 
parte practice under 37 CFR 1.131 which permits an 
applicant to show an actual date of invention prior to 
the effective date of a patent or literature reference 
applied under 35 
U.S.C. 102(a) or (e), as long as the 
patent is not a domestic patent claiming the same patentable 
invention. Ex parte Standish, 10 USPQ2d 
1454, 1457 (Bd. Pat. App. & Inter. 1988) (An application 
claim to the “same patentable invention” claimed 
in a domestic patent requires interference rather than 
an affidavit under 37 CFR 1.131 to antedate the 
patent. The term “same patentable invention” encompasses 
a claim that is either anticipated by or obvious 
in view of the subject matter recited in the patent 
claim.). Subject matter which is available as prior art 
only under 35 
U.S.C. 102(g) is by definition made 
before the applicant made his invention and is therefore 
not open to further inquiry under 37 CFR 1.131.



IV. LOST COUNTS IN AN INTERFERENCE 
ARE NOT, PER SE, STATUTORY PRIOR 
ART

Loss of an interference count alone does not make 
its subject matter statutory prior art to losing party; 
however, lost count subject matter that is available as 
prior art under 35 U.S.C. 102 may be used alone or in 
combination with other references under 35 U.S.C. 
103. But see In re Deckler, 977 F.2d 1449, 
24 
USPQ2d 1448 (Fed. Cir. 1992) (Under the principles 
of res judicata and collateral estoppel, Deckler 
was not entitled to claims that were patentably indistinguishable 
from the claim lost in interference even 
though the subject matter of the lost count was not 
available for use in an obviousness rejection under 
35 
U.S.C. 103.).

2138.02“The Invention Was Made in 
This Country” 

An invention is made when there is a conception 
and a reduction to practice. Dunn v. Ragin, 50 USPQ 
472, 474 (Bd. Pat. Inter. 1941). Prior art under 35 
U.S.C. 102(g) is limited to an invention that is made. 
In re Katz, 687 F.2d 450, 454, 215 USPQ 14, 
17 
(CCPA 1982) (the publication of an article, alone, 
is not deemed a constructive reduction to practice, and 
therefore its disclosure does not prove that any invention 
within the meaning of 35 U.S.C. 102(g) has ever 
been made). 

Subject matter under 35 U.S.C. 102(g) is available 
only if made in this country. 35 U.S.C. 104. Kondo v.
Martel, 220 USPQ 47 (Bd. Pat. Inter. 1983) (acts of 
conception, reduction to practice and diligence must 
be demonstrated in this country). Compare Colbert v.
Lofdahl, 21 USPQ2d 1068, 1071 (Bd. Pat. App. & 
Inter. 1991) (“[i]f the invention is reduced to practice 
in a foreign country and knowledge of the invention 
was brought into this country and disclosed to others, 
the inventor can derive no benefit from the work done 
abroad and such knowledge is merely evidence of 
conception of the invention”).

 In accordance with 35 U.S.C. 102(g)(1), a party 
involved in an interference proceeding under 
35 
U.S.C. 135 or 291 may establish a date of invention 
under 35 
U.S.C. 104. 35 U.S.C. 104, as amended 
by GATT (Public Law 103-465, 108 Stat. 4809 
(1994)) and NAFTA (Public Law 103-182, 107 Stat. 
2057 (1993)), provides that an applicant can establish 
a date of invention in a NAFTA member country on or 
after December 8, 1993 or in WTO member country 
other than a NAFTA member country on or after January 
1, 1996. Accordingly, an interference count may 
be won or lost on the basis of establishment of invention 
by one of the parties in a NAFTA or WTO member 
country, thereby rendering the subject matter of 
that count unpatentable to the other party under the 
principles of res judicata and collateral estoppel, even 
though such subject matter is not available as statutory 
prior art under 35 U.S.C. 102(g). See MPEP 
§
 
2138.01 regarding lost interference counts which 
are not statutory prior art. 




 

2138.03“By Another Who Has Not Abandoned, 
Suppressed, or Concealed 
It” 

35 U.S.C. 102(g) generally makes available as prior 
art within the meaning of 35 U.S.C. 103, the prior 
invention of another who has not abandoned, suppressed 
or concealed it. In re Bass, 474 F.2d 1276, 
177 USPQ 178 (CCPA 1973); In re Suska, 589 F.2d 
527, 200 USPQ 497 (CCPA 1979) (The result of 
applying the suppression and concealment doctrine is 
that the inventor who did not conceal (but was the de 
facto last inventor) is treated legally as the first to 
invent, while the de facto first inventor who suppressed 
or concealed is treated as a later inventor. The 
de facto first inventor, by his suppression and concealment, 
lost the right to rely on his actual date of invention 
not only for priority purposes, but also for 
purposes of avoiding the invention of the counts as 
prior art.).

“The courts have consistently held that an invention, 
though completed, is deemed abandoned, suppressed, 
or concealed if, within a reasonable time 
after completion, no steps are taken to make the 
invention publicly known. Thus failure to file a patent 
application; to describe the invention in a publicly 
disseminated document; or to use the invention publicly, 
have been held to constitute abandonment, suppression, 
or concealment.” Correge v. Murphy, 
705 
F.2d 1326, 1330, 217 USPQ 753, 756 (Fed. Cir. 
1983) (quoting International Glass Co. v. United 
States, 408 F.2d 395, 403, 159 USPQ 434, 441 (Ct. Cl. 
1968)). In Correge, an invention was actually reduced 
to practice, 7 months later there was a public disclosure 
of the invention, and 8 months thereafter a patent 
application was filed. The court held filing a patent 
application within 1 year of a public disclosure is not 
an unreasonable delay, therefore reasonable diligence 
must only be shown between the date of the actual 
reduction to practice and the public disclosure to 
avoid the inference of abandonment.

DURING AN INTERFERENCE PROCEEDING, 
AN INFERENCE OF SUPPRESSION OR CONCEALMENT 
MAY ARISE FROM DELAY IN 
FILING PATENT APPLICATION

Once an invention is actually reduced to practice an 
inventor need not rush to file a patent application. 
Shindelar v. Holdeman, 628 F.2d 1337, 1341, 
207 
USPQ 112, 116 (CCPA 1980). The length of time 
taken to file a patent application after an actual reduction 
to practice is generally of no consequence except 
in an interference proceeding. Paulik v. Rizkalla, 
760 
F.2d 1270, 1271, 226 USPQ 225, 226 (Fed. Cir. 
1985) (suppression or concealment may be deliberate 
or may arise due to an inference from a “too long” 
delay in filing a patent application). Peeler v. Miller, 
535 F.2d 647, 656, 190 USPQ 117,124 (CCPA 1976) 
(“mere delay, without more, is not sufficient to establish 
suppression or concealment.” “What we are 
deciding here is that Monsanto’s delay is not ‘merely 
delay’ and that Monsanto's justification for the delay 
is inadequate to overcome the inference of suppression 
created by the excessive delay.” The word 
“mere” does not imply a total absence of a limit on the 
duration of delay. Whether any delay is “mere” is 
decided only on a case-by-case basis.).

Where a junior party in an interference relies upon 
an actual reduction to practice to demonstrate first 
inventorship, and where the hiatus in time between 
the date for the junior party's asserted reduction to 
practice and the filing of its application is unreasonably 
long, the hiatus may give rise to an inference that 
the junior party in fact suppressed or concealed the 
invention and the junior party will not be allowed to 
rely upon the earlier actual reduction to practice. 
Young v. Dworkin, 489 F.2d 1277, 1280 n.3, 
180 
USPQ 388, 391 n.3 (CCPA 1974) (suppression 
and concealment issues are to be addressed on a case-
by-case basis). 

SUPPRESSION OR CONCEALMENT NEED 
NOT BE ATTRIBUTED TO INVENTOR

Suppression or concealment need not be attributed 
to the inventor. Peeler v. Miller, 535 F.2d 647, 653-54, 
190 USPQ 117, 122 (CCPA 1976) (“four year delay 
from the time an inventor … completes his work … 
and the time his assignee-employer files a patent 
application is, prima facie, unreasonably long in an 
interference with a party who filed first”); Shindelar 
v. Holdeman, 628 F.2d 1337, 1341-42, 207 USPQ 
112, 116-17 (CCPA 1980) (A patent attorney’s workload 
will not preclude a holding of an unreasonable 
delay—a total of 3 months was identified as possible 
of excuse in regard to the filing of an application.).




 

INFERENCE OF SUPPRESSION OR CONCEALMENT 
IS REBUTTABLE

Notwithstanding a finding of suppression or concealment, 
a constructive reduction to practice such as 
renewed activity just prior to other party’s entry into 
field coupled with the diligent filing of an application 
would still cause the junior party to prevail. Lutzker v.
Plet, 843 F.2d 1364, 1367-69, 6 USPQ2d 1370, 1371-
72 (Fed. Cir. 1988) (activities directed towards commercialization 
not sufficient to rebut inference); 
Holmwood v. Cherpeck, 2 USPQ2d 1942, 1945 (Bd. 
Pat. App. & Inter. 1986) (the inference of suppression 
or concealment may be rebutted by showing activity 
directed to perfecting the invention, preparing the 
application, or preparing other compounds within the 
scope of the generic invention); Engelhardt v. Judd, 
369 F.2d 408, 411, 151 USPQ 732, 735 (CCPA 1966) 
(“We recognize that an inventor of a new series of 
compounds should not be forced to file applications 
piecemeal on each new member as it is synthesized, 
identified and tested for utility. A reasonable 
amount 
of time should be allowed for completion 
of 
the 
research project on the whole series of new 
compounds, and a further reasonable time period 
should then be allowed for drafting and filing the 
patent application(s) thereon.”); Bogoslowsky v. Huse, 
142 F.2d 75, 77, 61 USPQ 349, 351 (CCPA 1944) 
(The doctrine of suppression and concealment is not 
applicable to conception without an actual reduction 
to practice.).

ABANDONMENT

A finding of suppression or concealment may not 
amount to a finding of abandonment wherein a right 
to a patent is lost. Steierman v. Connelly, 197 USPQ 
288, 289 (Comm'r Pat. 1976); Correge v. Murphy, 
705 
F.2d 1326, 1329, 217 USPQ 753, 755 (Fed. Cir. 
1983) (an invention cannot be abandoned until it is 
first reduced to practice). 

2138.04“Conception” [R-5]

Conception has been defined as “the complete performance 
of the mental part of the inventive act” and 
it is “the formation in the mind of the inventor of a 
definite and permanent idea of the complete and operative 
invention as it is thereafter to be applied in practice….” 
Townsend v. Smith, 36 F.2d 292, 295, 4 USPQ 
269, 271 (CCPA 1930). “[C]onception is established 
when the invention is made sufficiently clear to 
enable one skilled in the art to reduce it to practice 
without the exercise of extensive experimentation or 
the exercise of inventive skill.” Hiatt v. Ziegler, 
179 
USPQ 757, 763 (Bd. Pat. Inter. 1973). Conception 
has also been defined as a disclosure of an invention 
which enables one skilled in the art to reduce the 
invention to a practical form without “exercise of the 
inventive faculty.” Gunter v. Stream, 573 F.2d 77, 
197 
USPQ 482 (CCPA 1978). See also Coleman v. 
Dines, 754 F.2d 353, 224 USPQ 857 (Fed. Cir. 1985) 
(It is settled that in establishing conception a party 
must show possession of every feature recited in the 
count, and that every limitation of the count must 
have been known to the inventor at the time of the 
alleged conception. Conception must be proved by 
corroborating evidence.); Hybritech Inc. v. Monoclonal 
Antibodies Inc., 802 F. 2d 1367, 1376, 
231 
USPQ 81, 87 (Fed. Cir. 1986) (Conception is the 
“formation in the mind of the inventor, of a definite 
and permanent idea of the complete and operative 
invention, as it is hereafter to be applied in practice.”); 
Hitzeman v. Rutter, 243 F.3d 1345, 
58 
USPQ2d 1161 (Fed. Cir. 2001) (Inventor’s “hope” 
that a genetically altered yeast would produce antigen 
particles having the particle size and sedimentation 
rates recited in the claims did not establish conception, 
since the inventor did not show that he had a 
“definite and permanent understanding” as to whether 
or how, or a reasonable expectation that, the yeast 
would produce the recited antigen particles.).



I.CONCEPTION MUST BE DONE IN THE 
MIND OF THE INVENTOR 

The inventor must form a definite and permanent 
idea of the complete and operable invention to establish 
conception. Bosies v. Benedict, 27 F.3d 539, 543, 
30 USPQ2d 1862, 1865 (Fed. Cir. 1994) (Testimony 
by a noninventor as to the meaning of a variable of a 
generic compound described in an inventor’s notebook 
was insufficient as a matter of law to establish 
the meaning of the variable because the testimony 
was not probative of what the inventors conceived.).




 



II. AS LONG AS THE INVENTOR MAINTAINS 
INTELLECTUAL DOMINATION 
OVER MAKING THE INVENTION, 
IDEAS, SUGGESTIONS, AND MATERIALS 
MAY BE ADOPTED FROM OTHERS 

An inventor may consider and adopt ideas, suggestions 
and materials derived from many sources: a suggestion 
from an employee, a hired consultant or a 
friend even if the adopted material proves to be the 
key that unlocks the problem so long as the inventor 
“maintains intellectual domination of the work of 
making the invention down to the successful testing, 
selecting or rejecting….” Morse v. Porter, 155 USPQ 
280, 283 (Bd. Pat. Inter. 1965); Staehelin v. Secher, 
24 
USPQ2d 1513, 1522 (Bd. Pat. App. & Inter. 1992) 
(“evidence of conception naming only one of the 
actual inventive entity inures to the benefit of and 
serves as evidence of conception by the complete 
inventive entity”).



III. CONCEPTION REQUIRES CONTEMPORANEOUS 
RECOGNITION AND APPRECIATION 
OF THE INVENTION

There must be a contemporaneous recognition and 
appreciation of the invention for there to be conception. 
Silvestri v. Grant, 496 F.2d 593, 596, 181 
USPQ 
706, 708 (CCPA 1974) (“an accidental and 
unappreciated duplication of an invention does not 
defeat the patent right of one who, though later in time 
was the first to recognize that which constitutes the 
inventive subject matter”); Invitrogen, Corp. v. 
Clontech Laboratories, Inc., 429 F.3d 1052, 1064, 77 
USPQ2d 1161, 1169 (Fed. Cir. 2005)(In situations 
where there is unrecognized accidental duplication, 
establishing conception requires evidence that the 
inventor actually made the invention and understood 
the invention to have the features that comprise the 
inventive subject matter at issue). Langer v. Kaufman, 
465 
F.2d 915, 918, 175 USPQ 172, 174 (CCPA 
1972) (new form of catalyst was not recognized when 
it was first produced; conception cannot be established 
nunc pro tunc). However, an inventor does not 
need to know that the invention will work for there to 
be complete conception. Burroughs Wellcome Co. v. 
Barr Labs., Inc., 40 F.3d 1223, 1228, 32 USPQ2d 
1915, 1919 (Fed. Cir. 1994) (Draft patent application 
disclosing treatment of AIDS with AZT reciting dosages, 
forms, and routes of administration was sufficient 
to collaborate conception whether or not the 
inventors believed the inventions would work based 
on initial screening tests.) Furthermore, the inventor 
does not need to appreciate the patentability of the 
invention. Dow Chem. Co. v. Astro-Valcour, Inc., 267 
F.3d 1334, 1341, 60 USPQ2d 1519, 1523 (Fed. Cir. 
2001).

The first to conceive of a species is not necessarily 
the first to conceive of the generic invention. In re Jolley, 
308 F.3d 1317, 1323 n.2, 64 USPQ2d 1901, 1905 
n.2 (Fed. Cir. 2002). Further, while conception of a 
species within a genus may constitute conception of 
the genus, conception of one species and the genus 
may not constitute conception of another species in 
the genus. Oka v. Youssefyeh, 849 F.2d 581, 
7 
USPQ2d 1169 (Fed. Cir. 1988) (conception of a 
chemical requires both the idea of the structure of the 
chemical and possession of an operative method of 
making it). See also Amgen v. Chugai Pharmaceutical 
Co., 927 F.2d 1200, 1206, 18 
USPQ2d 1016, 1021 
(Fed. Cir. 1991) (in the isolation of a gene, defining a 
gene by its principal biological property is not sufficient 
for conception absent an ability to envision the 
detailed constitution as well as a method for obtaining 
it); Fiers v. Revel, 984 F.2d 1164, 1170, 25 USPQ2d 
1601, 1605 (Fed. Cir. 1993) (“[b]efore reduction to 
practice, conception only of a process for making a 
substance, without conception of a structural or equivalent 
definition of that substance, can at most constitute 
a conception of the substance claimed as a 
process” but cannot constitute conception of the substance; 
as “conception is not enablement,” conception 
of a purified DNA sequence coding for a specific protein 
by function and a method for its isolation that 
could be carried out by one of ordinary skill in the art 
is not conception of that material).

On rare occasions conception and reduction to 
practice occur simultaneously. Alpert v. Slatin, 
305 
F.2d 891, 894, 134 USPQ 296, 299 (CCPA 1962). 
“[I]n some unpredictable areas of chemistry and biology, 
there is no conception until the invention has 
been reduced to practice.” MacMillan v. Moffett, 
432 
F.2d 1237, 1234-40, 167 USPQ 550, 552-553 
(CCPA 1970). See also Hitzeman v. Rutter, 243 F.3d 
1345, 58 USPQ2d 1161 (Fed. Cir. 2001) 




 

(conception 
simultaneous with reduction to practice 
where appellant lacked reasonable certainty that 
yeast’s performance of certain intracellular processes 
would result in the claimed antigen particles); Dunn v. 
Ragin, 50 
USPQ 472, 475 (Bd. Pat. Inter. 1941) (a 
new variety of asexually reproduced plant is conceived 
and reduced to practice when it is grown and 
recognized as a new variety). Under these circumstances, 
conception is not complete if subsequent 
experimentation reveals factual uncertainty which “so 
undermines the specificity of the inventor’s idea that 
it is not yet a definite and permanent reflection of the 
complete invention as it will be used in practice.” 
Burroughs Wellcome Co. v. Barr Labs., Inc., 40 F.3d 
1223, 1229, 32 USPQ2d 1915, 1920 (Fed. Cir. 1994).



IV. A PREVIOUSLY ABANDONED APPLICATION 
WHICH WAS NOT COPENDING 
WITH A SUBSEQUENT APPLICATION IS 
EVIDENCE ONLY OF CONCEPTION

An abandoned application with which no subsequent 
application was copending serves to abandon 
benefit of the application’s filing as a constructive 
reduction to practice and the abandoned application is 
evidence only of conception. In re Costello, 717 F.2d 
1346, 1350, 219 USPQ 389, 392 (Fed. Cir. 1983).

2138.05“Reduction to Practice” [R-5]

Reduction to practice may be an actual reduction or 
a constructive reduction to practice which occurs 
when a patent application on the claimed invention is 
filed. The filing of a patent application serves as conception 
and constructive reduction to practice of the 
subject matter described in the application. Thus the 
inventor need not provide evidence of either conception 
or actual reduction to practice when relying on 
the content of the patent application. Hyatt v. Boone, 
146 F.3d 1348, 1352, 47 USPQ2d 1128, 1130 (Fed. 
Cir. 1998). A reduction to practice can be done by 
another on behalf of the inventor. De Solms v. Schoenwald, 
15 USPQ2d 1507, 1510 (Bd. Pat. App. & Inter. 
1990). “While the filing of the original application 
theoretically constituted a constructive reduction to 
practice at the time, the subsequent abandonment of 
that application also resulted in an abandonment of 
the benefit of that filing as a constructive reduction to 
practice. The filing of the original application is, however, 
evidence of conception of the invention.” In re 
Costello, 717 F.2d 1346, 1350, 219 USPQ 389, 392 
(Fed. Cir. 1983)(The second application was not co-
pending with the original application and it did not 
reference the original application. Because of the 
requirements of 35 U.S.C. 120 had not been satisfied, 
the filing of the original application was not recognized 
as constructive reduction to practice of the 
invention.).

I.CONSTRUCTIVE REDUCTION TO 
PRACTICE REQUIRES COMPLIANCE 
WITH 35 U.S.C. 112, FIRST PARAGRAPH

When a party to an interference seeks the benefit of 
an earlier-filed U.S. patent application, the earlier 
application must meet the requirements of 35 U.S.C. 
120 and 35 U.S.C. 112, first paragraph for the subject 
matter of the count. The earlier application must meet 
the enablement requirement and must contain a written 
description of the subject matter of the interference 
count. Hyatt v. Boone, 146 F.3d 1348, 1352, 
47 
USPQ2d 1128, 1130 (Fed. Cir. 1998). Proof of a 
constructive reduction to practice requires sufficient 
disclosure under the “how to use” and “how to make” 
requirements of 35 U.S.C. 112, first paragraph. Kawai 
v. Metlesics, 480 F.2d 880, 886, 178 USPQ 158, 163 
(CCPA 1973) (A constructive reduction to practice is 
not proven unless the specification discloses a practical 
utility where one would not be obvious. Prior art 
which disclosed an anticonvulsant compound which 
differed from the claimed compound only in the 
absence of a -CH2- group connecting two functional 
groups was not sufficient to establish utility of the 
claimed compound because the compounds were not 
so closely related that they could be presumed to have 
the same utility.). The purpose of the written description 
requirement is “to ensure that the inventor had 
possession, as of the filing date of the application 
relied on, of the specific subject matter later claimed 
by him.” In re Edwards, 568 F.2d 1349, 1351-52, 
196 
USPQ 465, 467 (CCPA 1978). The written 
description must include all of the limitations of the 
interference count, or the applicant must show that 
any absent text is necessarily comprehended in the 
description provided and would have been so understood 
at the time the patent application was filed. Furthermore, 
the written description must be sufficient, 
when the entire specification is considered, such that 




 

the “necessary and only reasonable construction” that 
would be given it by a person skilled in the art is one 
that clearly supports each positive limitation in the 
count. Hyatt v. Boone, 146 F.3d at 1354-55, 
47 
USPQ2d at 1130-1132 (Fed. Cir. 1998) (The claim 
could be read as describing subject matter other than 
that of the count and thus did not establish that the 
applicant was in possession of the invention of the 
count.). See also Bigham v. Godtfredsen, 857 F.2d 
1415, 1417, 8 
USPQ2d 1266, 1268 (Fed. Cir. 1988) 
(“[t]he generic term halogen comprehends a limited 
number of species, and ordinarily constitutes a sufficient 
written description of the common halogen species,” 
except where the halogen species are patentably 
distinct). 

II.REQUIREMENTS TO ESTABLISH ACTUAL 
REDUCTION TO PRACTICE

 “In an interference proceeding, a party seeking to 
establish an actual reduction to practice must satisfy a 
two-prong test: (1) the party constructed an embodiment 
or performed a process that met every element 
of the interference count, and (2) the embodiment or 
process operated for its intended purpose.” Eaton v. 
Evans, 204 F.3d 1094, 1097, 53 USPQ2d 1696, 1698 
(Fed. Cir. 2000).

The same evidence sufficient for a constructive 
reduction to practice may be insufficient to establish 
an actual reduction to practice, which requires a 
showing of the invention in a physical or tangible 
form that shows every element of the count. Wetmore 
v. Quick, 536 F.2d 937, 942, 190 USPQ 223, 227 
(CCPA 1976). For an actual reduction to practice, the 
invention must have been sufficiently tested to demonstrate 
that it will work for its intended purpose, but 
it need not be in a commercially satisfactory stage of 
development. See, e.g., Scott v. Finney, 34 F.3d 
1058, 1062, 32 USPQ2d 1115, 1118-19 (Fed. Cir. 
1994)(citing numerous cases wherein the character of 
the testing necessary to support an actual reduction to 
practice varied with the complexity of the invention 
and the 
problem it solved). If a device is so simple, 
and its purpose and efficacy so obvious, construction 
alone is sufficient to demonstrate workability. King 
Instrument Corp. v. Otari Corp., 767 F.2d 853, 860, 
226 USPQ 402, 407 (Fed. Cir. 1985).

For additional cases pertaining to the requirements 
necessary to establish actual reduction to practice see 
DSL Dynamic Sciences, Ltd. v. Union Switch & Signal, 
Inc., 928 F.2d 1122, 1126, 18 USPQ2d 1152, 
1155 (Fed. Cir. 1991) (“events occurring after an 
alleged actual reduction to practice can call into question 
whether reduction to practice has in fact 
occurred”);  Fitzgerald v. Arbib, 268 F.2d 763, 765-
66, 122 USPQ 530, 531-32 (CCPA 1959) (“the reduction 
to practice of a three-dimensional design invention 
requires the production of an article embodying 
that design” in “other than a mere drawing”); Birmingham 
v. Randall,
 
171 F.2d 957, 80 USPQ 371, 372 
(CCPA 1948) (To establish an actual reduction to 
practice of an invention directed to a method of making 
a product, it is not enough to show that the method 
was performed. “[S]uch an invention is not reduced 
to practice until it is established that the product made 
by the process is satisfactory, and [ ] this may require 
successful testing of the product.”). 

III.TESTING REQUIRED TO ESTABLISH 
AN ACTUAL REDUCTION TO PRAC-
TICE

“The nature of testing which is required to establish 
a reduction to practice depends on the particular facts 
of each case, especially the nature of the invention.” 
Gellert v. Wanberg, 495 F.2d 779, 783, 181 USPQ 
648, 652 (CCPA 1974) (“an invention may be tested 
sufficiently … where less than all of the conditions of 
actual use are duplicated by the tests”); Wells v. Fremont, 
177 USPQ 22, 24-5 (Bd. Pat. Inter. 1972) 
(“even where tests are conducted under ‘bench’ or 
laboratory conditions, those conditions must ‘fully 
duplicate each and every condition of actual use’ or if 
they do not, then the evidence must establish a relationship 
between the subject matter, the test condition 
and the intended functional setting of the invention,” 
but it is not required that all the conditions of all 
actual uses be duplicated, such as rain, snow, mud, 
dust and submersion in water). 

IV.REDUCTION TO PRACTICE RE-QUIRES 
RECOGNITION AND APPRE-CIATION 
OF THE INVENTION

The invention must be recognized and appreciated 
for a reduction to practice to occur. “The rule that conception 
and reduction to practice cannot be established 
nunc pro tunc simply requires that in order for 
an experiment to constitute an actual reduction to 




 

practice, there must have been contemporaneous 
appreciation of the invention at issue by the inventor…. 
Subsequent testing or later recognition may not 
be used to show that a party had contemporaneous 
appreciation of the invention. However, evidence of 
subsequent testing may be admitted for the purpose of 
showing that an embodiment was produced and that it 
met the limitations of the count.” Cooper v. Goldfarb, 
154 F.3d 1321, 1331, 47 USPQ2d 1896, 1904 (Fed. 
Cir. 1998) (citations omitted). Meitzner v. Corte, 537 
F.2d 524, 528, 190 USPQ 407, 410 (CCPA 1976) 
(there can be no conception or reduction to practice of 
a new form or of a process using such a new form of 
an otherwise old composition where there has been no 
recognition or appreciation of the existence of the 
new form); Estee Lauder, Inc. v. L’Oreal S.A., 129 
F.3d 588, 593, 44 USPQ2d 1610, 1615 (Fed. Cir. 
1997) (“[W]hen testing is necessary to establish utility, 
there must be recognition and appreciation that the 
tests were successful for reduction to practice to 
occur.” A showing that testing was completed before 
the critical date, and that testing ultimately proved 
successful, was held insufficient to establish a reduction 
to practice before the critical date, since the success 
of the testing was not appreciated or recognized 
until after the critical date.); Parker v. Frilette, 
462 
F.2d 544, 547, 174 USPQ 321, 324 (CCPA 1972) 
(“[an] inventor need not understand precisely why his 
invention works in order to achieve an actual reduction 
to practice”). 

V.RECOGNITION OF THE INVENTION BY 
ANOTHER MAY INURE TO THE BENEFIT 
OF THE INVENTOR

 “Inurement involves a claim by an inventor that, as 
a matter of law, the acts of another person should 
accrue to the benefit of the inventor.” Cooper v. Goldfarb, 
154 F.3d 1321, 1331, 47 USPQ2d 1896, 1904 
(Fed. Cir. 1998). Before a non-inventor’s recognition 
of the utility of the invention can inure to the benefit 
of the inventor, the following three-prong test must be 
met: (1) the inventor must have conceived of the 
invention, (2) the inventor must have had an expectation 
that the embodiment tested would work for the 
intended purpose of the invention, and (3) the inventor 
must have submitted the embodiment for testing 
for the intended purpose of the invention. Genentech 
Inc. v. Chiron Corp., 220 F.3d 1345, 1354, 
55 
USPQ2d 1636, 1643 (Fed. Cir. 2000). In Genentech, 
a non-inventor hired by the inventors to test 
yeast samples for the presence of the fusion protein 
encoded by the DNA construct of the invention recognized 
the growth-enhancing property of the fusion 
protein, but did not communicate this recognition 
to 
the inventors. The court found that because the 
inventors did not submit the samples for testing 
growth-promoting activity, the intended purpose of 
the invention, the third prong was not satisfied and the 
uncommunicated recognition of the activity of the 
fusion protein by the non-inventor did not inure to 
their benefit. See also Cooper v. Goldfarb, 240 F.3d 
1378, 1385, 57 USPQ2d 1990, 1995 (Fed. Cir. 2001) 
(Cooper sent to Goldfarb samples of a material for use 
in vascular grafts. At the time the samples were sent, 
Cooper was unaware of the importance of the fibril 
length of the material. Cooper did not at any time later 
convey to, or request from, Goldfarb any information 
regarding fibril length. Therefore, Goldfarb’s determination 
of the fibril lengths of the material could not 
inure to Cooper’s benefit.). 

VI.IN AN INTERFERENCE PROCEEDING, 
ALL LIMITATIONS OF A COUNT MUST 
BE REDUCED TO PRACTICE

The device reduced to practice must include every 
limitation of the count. Fredkin v. Irasek, 397 F.2d 
342, 158 USPQ 280, 285 (CCPA 1968); every limitation 
in a count is material and must be proved to 
establish an actual reduction to practice. Meitzner v. 
Corte, 537 F.2d 524, 528, 190 USPQ 407, 410. See 
also Hull v. Bonis, 214 USPQ 731, 734 (Bd. Pat. Inter. 
1982) (no doctrine of equivalents—remedy is a preliminary 
motion to amend the count to conform to the 
proofs). 

VII.CLAIMED INVENTION IS NOT ACT-
UALLY REDUCED TO PRACTICE UN-
LESS THERE IS A KNOWN UTILITY

Utility for the invention must be known at the time 
of the reduction to practice. Wiesner v. Weigert, 666 
F.2d 582, 588, 212 USPQ 721, 726 (CCPA 1981) 
(except for plant and design inventions); Azar v. 
Burns, 188 USPQ 601, 604 (Bd. Pat. Inter. 1975) (a 
composition and a method cannot be actually reduced 
to practice unless the composition and the product 
produced by the method have a practical utility); 




 

Ciric v. Flanigen, 511 F.2d 1182, 1185, 185 USPQ 
103, 105-6 (CCPA 1975) (“when a count does not 
recite any particular utility, evidence establishing a 
substantial utility for any purpose is sufficient to 
prove a reduction to practice”; “the demonstrated similarity 
of ion exchange and adsorptive properties 
between the newly discovered zeolites and known 
crystalline zeolites … have established utility for the 
zeolites of the count”); Engelhardt v. Judd, 369 F.2d 
408, 411, 151 USPQ 732, 735 (CCPA 1966) (When 
considering an actual reduction to practice as a bar to 
patentability for claims to compounds, it is sufficient 
to successfully demonstrate utility of the compounds 
in animals for somewhat different pharmaceutical 
purposes than those asserted in the specification for 
humans.); Rey-Bellet v. Engelhardt, 993 F.2d 1380, 
1384, 181 USPQ 453, 455 (CCPA 1974) (Two categories 
of tests on laboratory animals have been considered 
adequate to show utility and reduction to 
practice: first, tests carried out to prove utility in 
humans where there is a satisfactory correlation 
between humans and animals, and second, tests carried 
out to prove utility for treating animals.).

VIII.A PROBABLE UTILITY MAY NOT BE 
SUFFICIENT TO ESTABLISH UTILITY

A probable utility does not establish a practical utility, 
which is established by actual testing or where the 
utility can be “foretold with certainty.” Bindra v. 
Kelly, 206 USPQ 570, 575 (Bd. Pat. Inter. 1979) 
(Reduction to practice was not established for an 
intermediate useful in the preparation of a second 
intermediate with a known utility in the preparation of 
a pharmaceutical. The record established there was a 
high degree of probability of a successful preparation 
because one skilled in the art may have been motivated, 
in the sense of 35 U.S.C. 103, to prepare the 
second intermediate from the first intermediate. However, 
a strong probability of utility is not sufficient to 
establish practical utility.); Wu v. Jucker, 167 USPQ 
467, 472 (Bd. Pat. Inter. 1968) (screening test where 
there was an indication of possible utility is insufficient 
to establish practical utility). But see Nelson v. 
Bowler, 628 F.2d 853, 858, 206 USPQ 881, 885 
(CCPA 1980) (Relevant evidence is judged as a whole 
for its persuasiveness in linking observed properties 
to suggested uses. Reasonable correlation between the 
two is sufficient for an actual reduction to practice.).

2138.06“Reasonable Diligence” [R-1]

The diligence of 35 U.S.C. 102(g) relates to reasonable 
“attorney-diligence” and “engineering-diligence” 
(Keizer v. Bradley, 270 F.2d 396, 397, 
123 
USPQ 215, 216 (CCPA 1959)), which does not 
require that “an inventor or his attorney … drop all 
other work and concentrate on the particular invention 
involved….” Emery v. Ronden, 188 USPQ 264, 268 
(Bd. Pat. Inter. 1974). 

CRITICAL PERIOD FOR ESTABLISHING DILIGENCE 
BETWEEN ONE WHO WAS FIRST TO 
CONCEIVE BUT LATER TO REDUCE TO 
PRACTICE THE INVENTION

The critical period for diligence for a first conceiver 
but second reducer begins not at the time of conception 
of the first conceiver but just prior to the entry in 
the field of the party who was first to reduce to practice 
and continues until the first conceiver reduces to 
practice. Hull v. Davenport, 90 F.2d 103, 
105,
 
33 
USPQ 506, 508 (CCPA 1937) (“lack of diligence 
from the time of conception to the time immediately 
preceding the conception date of the second 
conceiver is not regarded as of importance except as it 
may have a bearing upon his subsequent acts”). What 
serves as the entry date into the field of a first reducer 
is dependent upon what is being relied on by the first 
reducer, e.g., conception plus reasonable diligence to 
reduction to practice (Fritsch v. Lin, 21 USPQ2d 
1731, 1734 (Bd. Pat. App. & Inter. 1991), Emery v. 
Ronden, 188 
USPQ 264, 268 (Bd. Pat. Inter. 1974)); 
an actual reduction to practice or a constructive reduction 
to practice by the filing of either a U.S. application 
(Rebstock v. Flouret, 191 USPQ 342, 345 (Bd. 
Pat. Inter. 1975)) or reliance upon priority under 
35 
U.S.C. 119 of a foreign application (Justus v. 
Appenzeller, 177 
USPQ 332, 339 (Bd. Pat. Inter. 
1971) (chain of priorities under 35 U.S.C. 119 and 
120, priority under 35 
U.S.C. 119 denied for failure to 
supply certified copy of the foreign application during 
pendency of the application filed within the twelfth 
month)). 




 

THE ENTIRE PERIOD DURING WHICH DILI-
GENCE IS REQUIRED MUST BE ACCOUNTED 
FOR BY EITHER AFFIRMATIVE ACTS OR ACCEPTABLE 
EXCUSES

An applicant must account for the entire period during 
which diligence is required. Gould v. Schawlow, 
363 F.2d 908, 919, 150 USPQ 634, 643 (CCPA 1966) 
(Merely stating that there were no weeks or months 
that the invention was not worked on is not enough.); 
In re Harry, 333 F.2d 920, 923, 142 USPQ 164, 
166 
(CCPA 1964) (statement that the subject matter 
“was diligently reduced to practice” is not a showing 
but a mere pleading). A 2-day period lacking activity 
has been held to be fatal. In re Mulder, 716 F.2d 1542, 
1545, 219 USPQ 189, 193 (Fed. Cir. 1983) (37 CFR 
1.131 issue); Fitzgerald v. Arbib, 268 F.2d 763, 766, 
122 USPQ 530, 532 (CCPA 1959) (Less than 1 month 
of inactivity during critical period. Efforts to exploit 
an invention commercially do not constitute diligence 
in reducing it to practice. An actual reduction to practice 
in the case of a design for a three-dimensional 
article requires that it should be embodied in some 
structure other than a mere drawing.); Kendall v. 
Searles, 173 F.2d 986, 993, 81 USPQ 363, 369 (CCPA 
1949) (Diligence requires that applicants must be specific 
as to dates and facts.). 

The period during which diligence is required must 
be accounted for by either affirmative acts or acceptable 
excuses. Rebstock v. Flouret, 191 USPQ 342, 345 
(Bd. Pat. Inter. 1975); Rieser v. Williams, 225 F.2d 
419, 423, 118 USPQ 96, 100 (CCPA 1958) (Being last 
to reduce to practice, party cannot prevail unless he 
has shown that he was first to conceive and that he 
exercised reasonable diligence during the critical 
period from just prior to opponent’s entry into the 
field); Griffith v. Kanamaru, 816 F.2d 624, 2 USPQ2d 
1361 (Fed. Cir. 1987) (Court generally reviewed cases 
on excuses for inactivity including vacation extended 
by ill health and daily job demands, and held lack of 
university funding and personnel are not acceptable 
excuses.); Litchfield v. Eigen, 535 F.2d 72, 190 USPQ 
113 (CCPA 1976) (budgetary limits and availability of 
animals for testing not sufficiently described); Morway 
v. Bondi, 203 F.2d 741, 749, 97 USPQ 318, 323 
(CCPA 1953) (voluntarily laying aside inventive concept 
in pursuit of other projects is generally not an 
acceptable excuse although there may be circumstances 
creating exceptions); Anderson v. Crowther,
152 USPQ 504, 512 (Bd. Pat. Inter. 1965) (preparation 
of routine periodic reports covering all accomplishments 
of the laboratory insufficient to show 
diligence); Wu v. Jucker, 167 USPQ 467, 472-73 (Bd. 
Pat. Inter. 1968) (applicant improperly allowed test 
data sheets to accumulate to a sufficient amount to 
justify interfering with equipment then in use on 
another project); Tucker v. Natta, 171 USPQ 494,498 
(Bd. Pat. Inter. 1971) (“[a]ctivity directed toward the 
reduction to practice of a genus does not establish, 
prima facie, diligence toward the reduction to practice 
of a species embraced by said genus”); Justus v. 
Appenzeller, 177 USPQ 332, 340-1 (Bd. Pat. Inter. 
1971) (Although it is possible that patentee could 
have reduced the invention to practice in a shorter 
time by relying on stock items rather than by designing 
a particular piece of hardware, patentee exercised 
reasonable diligence to secure the required hardware 
to actually reduce the invention to practice. “[I]n 
deciding the question of diligence it is immaterial that 
the inventor may not have taken the expeditious 
course….”).

WORK RELIED UPON TO SHOW REASONABLE 
DILIGENCE MUST BE DIRECTLY RELATED 
TO THE REDUCTION TO PRACTICE

The work relied upon to show reasonable diligence 
must be directly related to the reduction to practice 
of 
the invention in issue. Naber v. Cricchi, 567 F.2d 
382, 384, 196 USPQ 294, 296 (CCPA 1977), cert. 
denied, 439 U.S. 826 (1978). See also Scott v. 
Koyama, 281 
F.3d 1243, 1248-49, 61 USPQ2d 1856, 
1859 
(Fed. Cir. 2002) (Activities directed at building 
a plant to practice the claimed process of producing 
tetrafluoroethane on a large scale constituted 
efforts 
toward actual reduction to practice, and thus 
were evidence of diligence. The court distinguished 
cases where diligence was not found because inventors 
either discontinued development or failed to complete 
the invention while pursuing financing or other 
commercial activity.); In re Jolley, 308 F.3d 1317, 
1326-27, 64 USPQ2d 1901, 1908-09 (Fed. Cir. 2002) 
(diligence found based on research and procurement 
activities related to the subject matter of the interference 
count). “[U]nder some circumstances an inventor 
should also be able to rely on work on closely 
related inventions as support for diligence toward the 
reduction to practice on an invention in issue.” Ginos 




 

v. Nedelec, 220 USPQ 831, 836 (Bd. Pat. Inter. 1983) 
(work on other closely related compounds that were 
considered to be part of the same invention and which 
were included as part of a grandparent application). 
“The work relied upon must be directed to attaining a 
reduction to practice of the subject matter of the 
counts. It is not sufficient that the activity relied on 
concerns related subject matter.” Gunn v. Bosch, 
181 
USPQ 758, 761 (Bd. Pat. Inter. 1973) (An actual 
reduction to practice of the invention at issue which 
occurred when the inventor was working on a different 
invention “was fortuitous, and not the result of 
a 
continuous intent or effort to reduce to practice 
the 
invention here in issue. Such fortuitousness is 
inconsistent with the exercise of diligence toward 
reduction to practice of that invention.” 181 
USPQ at 
761. Furthermore, evidence drawn towards work on 
improvement of samples or specimens generally 
already in use at the time of conception that are but 
one element of the oscillator circuit of the count does 
not show diligence towards the construction and testing 
of the overall combination.); Broos v. Barton, 142 
F.2d 690, 691, 61 USPQ 447, 448 (CCPA 1944) 
(preparation of application in U.S. for foreign filing 
constitutes diligence); De Solms v. Schoenwald, 
15 
USPQ2d 1507 (Bd. Pat. App. & Inter. 1990) (principles 
of diligence must be given to inventor’s circumstances 
including skill and time; requirement of 
corroboration applies only to testimony of inventor); 
Huelster v. Reiter, 168 F.2d 542, 78 USPQ 82 (CCPA 
1948) (if inventor was not able to make an actual 
reduction to practice of the invention, he must also 
show why he was not able to constructively reduce 
the invention to practice by the filing of an application).


DILIGENCE REQUIRED IN PREPARING AND 
FILING PATENT APPLICATION

The diligence of attorney in preparing and filing 
patent application inures to the benefit of the inventor. 
Conception was established at least as early as the 
date a draft of a patent application was finished by a 
patent attorney on behalf of the inventor. Conception 
is less a matter of signature than it is one of disclosure. 
Attorney does not prepare a patent application 
on behalf of particular named persons, but on behalf 
of the true inventive entity. Six days to execute and 
file application is acceptable. Haskell v. Coleburne, 
671 F.2d 1362, 213 USPQ 192, 195 (CCPA 1982). 
See also Bey v. Kollonitsch, 866 F.2d 1024, 231 
USPQ 
967 (Fed. Cir. 1986) (Reasonable diligence is all that 
is required of the attorney. Reasonable diligence is 
established if attorney worked reasonably hard on the 
application during the continuous critical period. If 
the attorney has a reasonable backlog of unrelated 
cases which he takes up in chronological order and 
carries out expeditiously, that is sufficient. Work on a 
related case(s) that contributed substantially to the 
ultimate preparation of an application can be credited 
as diligence.).

END OF DILIGENCE PERIOD IS MARKED BY 
EITHER ACTUAL OR CONSTRUCTIVE REDUCTION 
TO PRACTICE

"[I]t is of no moment that the end of that period [for 
diligence] is fixed by a constructive, rather than an 
actual, reduction to practice." Justus v. Appenzeller, 
177 USPQ 332, 340-41 (Bd. Pat. Inter. 1971).