Serum and bile concentrations of temocillin were measured after intravenous administration of 1g twice daily to 16 patients with biliary tract infections. The concentration of temocillin in the bile showed high inter-individual variations; however, in patients drug concentrations were attained which were considerably higher than the minimum inhibitory concentrations of the biliary tract pathogens identified throughout the study period. All the patients admitted to the study were treated successfully by temocillin, with the tolerance of the drug being very good, and no side effects or drug-related deteriorations of laboratory data being reported.