In AbTox, Inc. v. Exitron Corp., 122 F.3d 1019 (Fed.Cir.1997), the Court applied the reasoning of the Supreme Court in Eli Lilly & Co. v. Medtronic, Inc., 496 U.S. 661, 669, 110 S.Ct. 2683, 110 L.Ed.2d 605 (1990). After being sued for patent infringement, AbTox, Inc. ("AbTox") alleged in a counterclaim that Exitron Corporation and MDT Corporation ("defendants") infringed its U.S. Patent No. 4,321,232 (the "'232 patent"). The '232 patent claimed a medical device used in sterilizing medical instruments. AbTox, 122 F.3d at 1020-21. Defendants moved for summary judgment of noninfringement, claiming that their use of the invention claimed in the '232 patent in pursuit of FDA approval for a plasma sterilizer was covered by the safe harbor provision of section 271(e)(1). Id. at 1027. After the district court granted the motion, AbTox appealed. The patented medical device in AbTox presented an issue not confronted in Eli Lilly, due to the varying levels of FDA regulation for different medical devices. The Court observed that although all three categories of medical devices, Classes I, II, and III, are subject to varying levels of FDA premarket approval, only Class III medical devices are eligible for patent term extension under section 156. Id. at 1028-29.