21 CFR § 320.35 - Requirements for in vitro testing of each batch.
---
identifier: "/us/cfr/t21/s320.35"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "21 CFR § 320.35 - Requirements for in vitro testing of each batch."
title_number: 21
title_name: "Food and Drugs"
section_number: "320.35"
section_name: "Requirements for in vitro testing of each batch."
chapter_name: "FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES"
subchapter_number: "D"
subchapter_name: "DRUGS FOR HUMAN USE"
part_number: "320"
part_name: "BIOAVAILABILITY AND BIOEQUIVALENCE REQUIREMENTS"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "21 U.S.C. 321, 351, 352, 355, 371."
cfr_part: "320"
---
# 320.35 Requirements for in vitro testing of each batch.
If a bioequivalence requirement specifies a currently available in vitro test or an in vitro bioequivalence standard comparing the drug product to a reference standard, the manufacturer shall conduct the test on a sample of each batch of the drug product to assure batch-to-batch uniformity.
[42 FR 1635, Jan. 7, 1977. Redesignated at 57 FR 18001, Apr. 28, 1992]