This guidance describes FDA’s compliance policy related to the retention of reserve samples of the test article and reference standard used in an in vivo bioavailability (BA) and in vivo or in vitro bioequivalence (BE) study. Specifically, this guidance:

• Addresses the requirement at 21 CFR 320.38(c) to retain reserve samples of sufficient quantity to permit FDA to perform five times all the release tests required in an application or supplemental application

• Describes the conditions under which the Agency does not generally intend to take enforcement action against an applicant or contract research organization (CRO) for retaining less than the quantity of reserve samples of the test article and reference standard that were used in the BA or BE study as specified in 21 CFR 320.38(c).