Abbott Laboratories (Abbott), the successor to Therasense, Inc. (defendant), obtained patents for disposable glucose test strips for diabetes. Becton-Dickinson, Inc. brought suit, seeking a declaratory judgment that Abbott’s patents were invalid. In its patent application, Abbott had stated that its invention required a protective membrane, and that such a membrane was not merely optional or preferred. Unbeknownst to the U.S. Patent and Trademark Office (PTO), this position was in contrast to a previous assertion by Abbott’s European patent counsel to the European Patent Office (EPO). The patent counsel had stated that the invention was optional, but preferable. Abbott did not tell the PTO about the statement before the EPO. As a result, the United States District Court for the Northern District of California (District Court) held the glucose test strip patents unenforceable due to inequitable conduct on the part of Abbott. A panel of the United States Court of Appeals for the Federal Circuit affirmed, but then granted rehearing en banc.