Temocillin concentrations were determined in the gallbladder bile and/or common bile duct bile obtained intraoperatively from 20 patients, and in the T-tube bile of 5 postoperative patients. Blood samples were also obtained for determining the concomitant serum antibiotic concentrations. In 6 patients with cholelithiasis, but without common bile duct obstruction or acute infection, the mean temocillin concentrations were 890 mg/L in gallbladder bile and 1030 mg/L in common bile duct bile. In the group of 6 patients with common bile duct obstruction, the antibiotic concentrations ranged between 5.6 and 88 mg/L (mean 38.8 mg/L) in gallbladder bile and between 'undetectable' and 700 mg/L in common bile duct bile. In patients with biliary sepsis, a further reduction in temocillin bile concentrations was observed, and postoperatively, the T-tube bile temocillin concentrations were in the range of 21 to 460 mg/L (mean 130 mg/L). The clinical efficacy of temocillin in the 7 patients with acute cholecystitis was judged to be satisfactory. Our results suggest that temocillin may be considered as a potentially useful antibiotic in the treatment of patients with biliary tract sepsis caused by susceptible organisms.