Fifty patients (29 females) undergoing ERCP were studied prospectively for the occurrence of bacteremia associated with this endoscopic procedure. Each patient had blood samples drawn for aerobic and anaerobic cultures before endoscopy, after entering the duodenum, 5 and 15 minutes after cannulation of the papilla of Vater. Subcultures were made at 24 and 48 hours for a total of 1,200 cultures. No positive cultures were obtained in 48 patients. One patient developed a Staphylococcus epidermidis bacteremia during the procedure. The cleansing technic for the instruments consisted of alcohol and water only. Prophylactic antiobiotics were not administered. In contrast to other gastrointestinal procedures, our results suggest that bacteremia is an uncommon occurrence in ERCP despite the longer duration of the procedure and instrumentation of a sterile duct system.