Bacterial infection of the bile system appears to be an important factor in the formation of stones. In view of the hypothesis that strains of E. c. form an essential factor in infections of the bile ducts, an attempt has been made to determine the connection between infections of the bile ducts and the adherence of E. c. to the epithelium of the gallbladder. The research covered 148 patients operated electively for cholecystolithiasis (121), cholecystocholedocholithiasis (26) and recurrent lithiasis (1). In bile collected from the gallbladder in the course of the operation, E. coli strains were isolated. Cholangioscopy performed in 26 patients enabled the macroscopic evaluation and grading of inflammatory lesions of bile duct mucosa. The mucosa of the gallbladder was evaluated histologically. The adherence test was performed using homologous and heterologous strains of E. c. isolated from the bile of gallstone patients. The adherence occurred most frequently in the neck of the gallbladder (71-100%) in those patients in whom an infectious process of the bile ducts mucosa was endoscopically diagnosed. The adherence of bacteria to the epithelium of the gallbladder did not depend on the type of inflammation (acute, chronic).