Bile samples from the common duct were collected at cholecystectomy and cultivated aerobically and anaerobically. Two groups of patients were studied, patients with juxta-papillary duodenal diverticula and patients without diverticula. All patients had chronic cholecystitis and concrements in the gallbladder, but no biliary obstruction. A significantly higher incidence of positive cultures was found in patients with diverticula than in the control group. The positive samples contained bacterial species belonging to the intestinal flora. We propose an ascending route of infection and assume that bacteria may play a role in the formation of gallstones so often seen in patients with juxta-papillary duodenal diverticula.