A party may not rely on an actual reduction to practice if
the invention was subsequently suppressed or concealed.
35 U.S.C. § 102(g). Mere delay alone will not establish
suppression or concealment. Young v. Dworkin, 489 F.2d 1277,
1281, 180 USPQ 388, 391-2 (CCPA 1974). However, an intent to
suppress or conceal may be inferred from an unreasonable lapse of
time between the actual and constructive reductions to practice.
Peeler v. Miller, 535 F.2d 647, 653, 190 USPQ 117, 122 (CCPA
1976). The inference can be negated, e.g., by disclosing the
invention to the public (Palmer v. Dudzik, 481 F.2d 1377, 1386,
178 USPQ 608, 615 (CCPA 1973)); or by improving or perfecting the
invention within a reasonable time after the reduction to
practice, and disclosing that improvement in an application
promptly filed thereafter (see Horwath v. Lee, 564 F.2d 948, 950,
195 USPQ 701, 704 (CCPA 1977)).
What constitutes an unreasonable lapse of time must be
determined on a case-by-case basis. In Shindelar v. Holdeman,
628 F.2d 1337, 207 USPQ 112 (CCPA 1980), the CCPA found a 29
month delay between an actual reduction to practice and a
constructive reduction to practice to be an unreasonable length
of time. To negate the inference, the junior party in Shindelar
had presented evidence of some activity during the 29 month
period. The CCPA, however was not persuaded that such activity
excused the delay and thus agreed with the board that the junior
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