On March 22, 2010, the Federal Circuit issued an important en banc decision upholding a separate written description requirement under 35 U.S.C. § 112. In Ariad Pharmaceuticals, Inc. v. Eli Lilly and Co., the Court rejected the patent owner's contention that the written description requirement is simply a part of the enablement requirement, which requires that the specification teach how to make and use the invention. The Court had received over 25 amicus briefs. The decision keeps intact the ability of patent infringement defendants to use the written description requirement to force a narrow construction of broad claims and to invalidate genus claims where the written description is expressly or implicitly limited to a species.