Viskase Cos., Inc. v. World Pac Int'l AG, No. 09 C 5022, Slip Op. (N.D. Ill. Feb. 3, 2011) (Bucklo, J.).

Judge Bucklo granted declaratory judgment plaintiff Viskase's motion for summary judgment of invalidity and denied the remaining cross-summary judgment motions as moot in this patent dispute involving food casings that prevent the loss of weight, flavor and taste. The Court previously construed "impermeable" to mean that the casing did not allow any measurable loss of weight, flavor or moisture. Instead of addressing each of Viskase's arguments element-by-element, declaratory judgment defendant World Pac put "all of its eggs in one basket." The Court denied World Pac's earlier summary judgment motion regarding infringement largely because of World Pac's failure to test the alleged impermeability of Viskase's accused products. World Pac, therefore, argued that because Viskase had not tested sausages covered by the prior art patent, it could not succeed.

But the Court explained that "what is good for the goose is not always good for the gander." The Court held that there was no authority requiring that a party test alleged anticipatory prior art patents to prove that they read on the asserted patent. While there was some appeal to World Pac's argument, it was unsuccessful. An accused infringer is not required to test prior art products. Furthermore, World Pac's own expert had conceded that the relevant claim elements of the patent-in-suit were disclosed in the prior art patent.