Forty-five patients with sphincter of Oddi stenosis had specimens of common bile duct cultured during ERCP before either sphincteroplasty or endoscopic sphincterotomy. All had sterile bile before sphincter ablation. Bile was recultured 6 to 36 months later during endoscopy at which time 70 percent of the sphincterotomy and 76 percent of the sphincteroplasty patients had bile colonized principally by enteric organisms. Growth was heavy to moderate in most of the patients and contained few nasopharyngeal organisms. Despite bactobilia, no patient had symptomatic cholangitis, presumably due to excellent drainage of bile. The most likely source of the bactobilia is from direct extension of duodenal organisms into the common bile duct.