A high-performance liquid chromatography (HPLC) procedure has been developed for the determination of azapropazone and its 6-hydroxy metabolite in plasma and urine. The procedure is simple and rapid since extraction of the drug and its metabolite is not required. Plasma proteins are precipitated with methanol, and the supernate is injected onto a reverse-phase HPLC column. With photometric detection at 254 nm, the procedure can determine as little as 0.4 micrograms/ml azapropazone in plasma or urine and 1.5-3 micrograms/ml of the metabolite in urine, depending upon the level of interference. The procedure has been used successfully in single-dose pharmacokinetic and bioavailability studies of azapropazone dosage forms.