Boehringer Ingelheim Vetmedica Inc. v. Schering-Plough Corp.
The invention related to the isolation of the virus that caused “Mystery swine disease” (a.k.a Porcine Reproductive Respiratory Syndrome – PRRS). The claim was directed to growing and isolating a particular virus. The alleged infringement was a similar technique for growing and isolating a similar virus. The defendants argued that there was no functional equivalency because the virus specified in the claim was pathogenic and the virus it was growing and isolating was not. The Federal Circuit disagreed and pointed out that when applying the function, way result test to a claim element to determine whether there is infringement under the doctrine of equivalents, the issue to be decided was whether the element fulfilled the same function in the context of the claimed invention, not whether it was functionally equivalent in some other situation. The court found that pathogenicity was irrelevant to the question of whether the viruses were equivalent for the purpose of the method claimed.
 65 USPQ2d 1961 (Fed. Cir. 2003)