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Warner-Jenkinson Company v. Hilton Davis Chemical Co.

United States Supreme Court
520 U.S. 17 (1997)


Hilton Davis (plaintiff) sued Warner-Jenkinson (defendant) for infringing the ‘746 patent, which claimed a new method of purifying dye. During prosecution of the ‘746 patent, a claim limitation was added requiring that the process take place between pHs of 6.0 and 9.0. The pH 9.0 limitation was added to make the claim patentable in light of prior art. However, the exact reason for the pH 6.0 limitation was disputed by the parties Warner-Jenkinson used a similar process, except one that took place at a pH of 5.0. Because the accused Warner-Jenkinson process did not literally infringe, Hilton Davis alleged that it infringed under the doctrine of equivalents. The jury agreed and the Federal Circuit Court of Appeals affirmed the district court. Five of the twelve justices dissented, each arguing for a narrowed doctrine of equivalents. Warner-Jenkinson petitioned for a writ of certiorari, which was granted.

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