A sharply divided en banc U.S. Court of Appeals for the Federal Circuit significantly narrowed the scope of the patent misuse defense this week. In Princo Corp. v. International Trade Commission, a five judge majority drew a sharp line between general antitrust violations in which patents might be involved and a few well-delineated practices which can now constitute patent misuse rendering a patent unenforceable. Two judges concurred on a limited basis, and two judges strongly dissented.