What is a prima facie case of equivalence in patent examination?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

A prima facie case of equivalence is established when an examiner finds that a prior art element:

• (A) performs the function specified in the claim,
• (B) is not excluded by any explicit definition provided in the specification for an equivalent, and
• (C) is an equivalent of the means- (or step-) plus-function limitation.

The examiner should provide an explanation and rationale in the Office action as to why the prior art element is an equivalent. As stated in MPEP 2183: “If the examiner finds that a prior art element (A) performs the function specified in the claim, (B) is not excluded by any explicit definition provided in the specification for an equivalent, and (C) is an equivalent of the means- (or step-) plus-function limitation, the examiner should provide an explanation and rationale in the Office action as to why the prior art element is an equivalent.“