Warner-Jenkinson Company v. Hilton Davis Chemical Co.
United States Supreme Court
520 U.S. 17 (1997)
Hilton Davis (plaintiff) held a patent for a dye-purification process specifying a pH range of 6.0 to 9.0, added during prosecution partly to overcome prior art, and sued Warner-Jenkinson (defendant), which practiced a similar process at pH 5.0, for infringement under the doctrine of equivalents since there was no literal infringement; a jury and the Federal Circuit found infringement, with several Federal Circuit judges dissenting to urge narrowing the doctrine, and Warner-Jenkinson petitioned for certiorari challenging the doctrine's continued validity and scope.
Whether an unclear-purpose claim amendment made during patent prosecution creates a rebuttable presumption that the amendment was made to secure patentability, thereby eliminating the doctrine of equivalents for the amended portion of the claim.