Warner-Jenkinson Company, Inc. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997), was a United States Supreme Court decision in the area of patent law, affirming the continued vitality of the doctrine of equivalents while making some important refinements to the doctrine.

[1] The plaintiff Hilton Davis Chemical Co., a dyemaker, had developed an "ultrafiltration" process to purify dyes.

The defendant had developed a process using a solution with a pH level of 5.0, which was outside the range of the plaintiff's patent.

The Court, in an opinion by Justice Clarence Thomas, held that the doctrine of equivalents had not been eliminated by changes to the patent statute.

The case was remanded to the trial court to determine if the plaintiff could explain his lower pH limit.