The physiologic availability of five phenylbutazone formulations, all sugar-coated tablets, marketed in India was measured in a cross-over study with six healthy male volunteers by determining drug concentrations in plasma. Single doses of 100 mg were administered and pure drug powder was used as standard. Significant differences between the bioavailability of various products were determined despite large individual variations. Two formulations were found to give bioavailabilities of about 50% that of powder. Maximum concentrations of phenylbutazone in plasma appeared after 3-10 h depending on the preparation. Therapeutic differences in normal dosing schedule may be anticipated in case on the two poorly bioavailable products.