CFR›Title 21›Chapter I›Part 331›Subpart C ContainsSections 331.20–331.21CorpusDaily eCFRDisplayed edition2026-04-15Last updated2026-04-15 Subpart C—Testing Procedures Sections 331.20 § 331.20 Determination of percent contribution of active ingredients. 331.21 § 331.21 Test modifications. Previous B Subpart B—Active Ingredients Next D Subpart D—Labeling