The Ultrasonic Microprobe (UMP) (Toshiba Co.) has a diameter of 2.4 mm, and its tip can accept a 10, 15, and- or 20 MHz mechanical radial scanner. We used this probe transpapillarily for intraductal scanning of the biliary and pancreatic ducts through a duodenoscope in 37 patients. Thirty-one of the patients had biliary diseases: hepatolithiasis, 3; choledocholithiasis, 17; congenital choledocal dilation, 3; benign bile duct tumor, 4; bile duct cancer, 4. Six others had pancreatic diseases: chronic calcifying pancreatitis, 1; mucin-producing tumor, 5. Before this procedure, endoscopic papillotomy had been performed in all patients except the five who had mucin-producing pancreatic tumors. The normal bile-duct wall appeared as a three layered structure consisting of inner hyperechoic, middle hypoechoic, and outer hyperechoic layers. In the cases of cholangitis, the second layer of the wall appeared as a thickened and homogeneously hypoechoic layer; in cancer of the bile duct, the first and second layers of the wall appeared to have merged, forming a thickened, heterogeneously hypoechoic layer. The wall of the normal pancreatic duct presented the image of a hyperechoic layer. A mucin-producing tumor of the pancreas was accompanied by multiple tufty cycts and intracavital papillary growths. Transpapillary intraductal scanning with the UMP should prove usefull in the evaluation of billiary and pancreatic diseases when further mechanical improvement has been achieved.