The authors present their experience with antimicrobial prophylaxis using cephalosporin of the second generation--cefamandole--in biliary surgery. Cefamandole was administered to 28 patients operated for a biliary affection and hospitalized at the Surgical Clinic of the Third Medical Faculty in Prague. Cefamandole was administered after 8-hour intervals in 1 g doses up to 48 hours after the first dose. For antimicrobial prophylaxis patients were selected, included after previous investigations in the high risk group. In the patients in addition to microbiological examination of bile the cefamandole levels in bile and serum were compared. The presented results proved that cefamandole administration is justified in the prevention of infectious complications after operations of the gallbladder and biliary pathways because of its antibacterial and pharmacokinetic properties.