An experience with 1,421 biliary operations in a five-year period was evaluated retrospectively. Forty-one percent of the 22 deaths were due to septic causes. Thirty-three percent of all bile cultures were positive, and postoperative septic complications were 40 times more frequent in cases with positive bile cultures than in cases with negative cultures. This difference is attributed to internal contamination by the infected bile at the time of operation. Patients at high risk of such contamination can be identified preoperatively, and they should receive preoperative antibiotics. Characteristics of the group demonstrating biliary bacteremia in 60% or more of the cases were acute cholecystitis, common duct stones with or without jaundice, and age of 70 or more years.