The technical aspects of endoscopic ultrasonography (EUS) of the biliary tract are described. EUS was performed in 55 patients with biliary tract diseases (20 cases in the gallbladder, 23 in the choledochus, and 12 in the papilla of Vater). For ultrasonographic visualization of the whole biliary tract including the papilla of Vater, entry into the second portion of the duodenum was necessary. At the papilla of Vater, ultrasonographic scanning was started, to obtain images of the papilla of Vater and the intrapancreatic common bile duct. Then we began to withdraw the instrument slowly to the post-bulbar or bulbar region of the duodenum, obtaining ultrasonographic images of the common bile duct and gallbladder. With this scanning, ultrasonograms of the whole biliary tract could be obtained. Detection by EUS in all 11 cases of a small tumor of less than 30 mm in the biliary tract provided valuable information for the precise diagnosis. Thus, EUS has important indications in the detection of small lesions in the papilla of Vater, common bile duct, and gallbladder.