Using the isolated rabbit liver perfusion model, it could be shown that 11.1% of 10 mg of cefamandole added to the circulating blood were recovered in the 3 hours collected bile. The maximal biliary antibiotic activity averaged 214 +/- 37 microgram/ml. In humans a peak concentration of 19.0 +/- 6.1 microgram/ml could be measured in the aspirated duodenal fluid (n = 5) 1 hour after a single intravenous injection of 1 g of cefamandole. In 10 patients provided with a Kehr's drainage, a mean biliary peak of 141.4 +/- 86.4 microgram/ml was observed at the 2nd hour after administration of the same dose of cefamandole. Assays performed during cholecystectomy showed 1 after the intravenous injection of 1 g of cefamandole mean values of 64.0 +/- 18.0 microgram/ml in the gallbladder bile and 87.2 +/- 16.1 microgram/ml in the common duct bile. These data are compared with those obtained by administration of 11 other beta-lactamines under similar experimental and clinical conditions.