Warner-Jenkinson Co. v. Hilton Davis Chemical Co.

Two chemical companies fought over whether a dye purification process that used a slightly different pH still violated an existing patent. The Supreme Court said the doctrine of equivalents (a rule for deciding when a changed process is still too similar to a patented one) remains valid and affirmed.

This matters to inventors and manufacturers who try to avoid patent suits by making small technical changes. For example, changing one setting in a production process may not be enough if the new method is still basically the same.

The Supreme Court has finished this docket action. Businesses and lower courts will keep using the doctrine of equivalents in future patent fights over modified products and processes.

The Court said the doctrine of equivalents remains a valid way to judge whether a changed process still violates a patent. It affirmed.

Patent owners and companies making slightly modified products or processes are most affected. Small technical changes may still lead to a patent lawsuit.

The Supreme Court has finished this docket action. Future patent cases will use this rule when parties argue over whether a modified invention is still too similar.