The combination of a penicillin and an aminoglycoside has been recommended as the initial treatment of choice for patients with infections of the biliary tract. However, elderly, septic, patients with jaundice have a high incidence of renal problems. For this reason, amingolycoside treatment of these patients must be reevaluated as newer less nephrotoxic agents become available. We, therefore, performed a prospective, randomized trial of ampicillin plus tobramycin, cefoperazone and piperacillin in patients with biliary tract infections. During a 20 month period, 106 patients with acute cholecystitis (53) or cholangitis (53), or both, received one of these antibiotic regimens for a minimum of five days. In patients with acute cholecystitis, ampicillin plus tobramycin, cefoperazone and piperacillin had clinical cure rates of 85, 95 and 95 per cent, respectively. In patients with cholangitis, however, cure rates for the three regimens were 85, 56 (p less than 0.05 versus ampicillin plus tobramycin) and 60 per cent (not significant versus ampicillin plus tobramycin), respectively. Moreover, 13 per cent of the patients receiving cefoperazone had an increased prothrombin time and three of 39 patients receiving this antibiotic had clinical problems with bleeding. Nephrotoxicity was greatest in patients with cholangitis receiving ampicillin plus tobramycin, 10 per cent, as compared with 3 per cent in those who did not receive an aminoglycoside. This difference, however, was not statistically significant. It was concluded that piperacillin should be considered for antibiotic management of patients with acute cholecystitis and that further studies are necessary in patients with cholangitis to determine whether or not newer agents should replace penicillin and aminoglycoside combinations.