"The threshold issue in this appeal is whether "improper revival" may be raised as an invalidity defense in an action involving the infringement or validity of a patent. The district court, relying on 35 U.S.C. §§ 282(2) and (4), decided that question affirmatively. The district court also found that the APA provided a separate basis upon which to review the PTO’s revival of the ’215 patent. We conclude that "improper revival" may not be raised as a defense in an action involving the validity or infringement of a patent."

Aristocrat Technologies Australia Pty Limited v. International Game Technology,  Appeal No. 2008-1016 (Fed. Cir., Sept. 22, 2008).  The court did not address whether the Patent Act permits revival for unintentional delay.