The metabolism of acetaminophen and oxazepam in humans is mainly dependent on the microsomal capacity for glucuronide conjugation. The clearance of acetaminophen and the formation of metabolites were evaluated in 7 patients before and during concomitant administration of oxazepam 30 mg. The subjects received a single 500 mg dose of acetaminophen i.v. and concentrations in plasma were measured for 360 minutes and in urine for 24 h in order to estimate the production of metabolites. The single therapeutic dose of oxazepam had no effect on the clearance of acetaminophen or on formation of its metabolites.