The purpose of this guidance is to clarify circumstances under which the FDA’s Center for Drug Evaluation and Research (CDER) may refuse to file a new drug application (NDA) or supplemental NDA (21 CFR 314.101(d)) or a biologics license application (BLA) or supplemental BLA (21 CFR 601.2) for a therapeutic biological product regulated by CDER,2  and to underscore the importance of submitting a complete application to minimize the chance of a refuse-to-file (RTF) action by the FDA. In particular, this guidance focuses on the FDA’s policy for refusing to file an NDA under § 314.101(d)(3) when the NDA is incomplete because it does not on its face contain information required under section 505(b) of the Federal Food, Drug, and Cosmetic Act (FD&C Act) and 21 CFR 314.50