In a study of diazepam metabolism, diazepam 10 mg was administered i.m. to four patients who had biliary T-tube drainage. Blood and bile diazepam metabolite concentrations were measured for 12 hr. The expected fluctuations in blood diazepam concentrations were seen, and conjugated diazepam metabolites were present in human bile. Bile diazepam concentrations were insufficient to account for an enterohepatic circulation.