Nasobiliary double contrast radiography and nasobiliary cytological diagnosis via nasobiliary catheter were performed in 30 patients with biliary diseases to assess the diagnostic usefulness and limitations of the procedures. The results showed that the contour and fine mucosal pattern of the extrahepatic bile duct could be demonstrated adequately (88%) by nasobiliary double contrast radiography. In contrast, the intrahepatic bile duct could not be fully demonstrated (56%) by nasobiliary double contrast radiography because of its anatomical structure. On the other hand the fine reticular pattern of the mucosa was defined in each section of the gallbladder by nasobiliary double contrast radiography. This procedure is thus a valuable method for detection of mucosal lesions of the extrahepatic bile duct and gallbladder, especially carcinoma. The cell collection rate was not as high (59%) using conventional nasobiliary cytological diagnosis. Brush cytology via a nasobiliary catheter was shown to be a useful adjunct to other diagnostic procedures.