To overcome limitation of ultrasound diagnosis of pancreatic diseases, especially of malignancy, the use of an echoendoscope was investigated. The instruments were the prototype echoendoscopes type 1-3 manufactured by Olympus Co., Tokyo, Japan. The first prototype was a mirror-type radial sector scanner equipped to a gastrofiberscope . The 2nd and 3rd types were of similar construction except the use of a small transducer with an increased frequency (7 mm in diameter, 7.5 MHz) and of direct rotation of the transducer connected to the flexible shaft. To visualize the pancreas effectively, a liquid-filled stomach method to use deaerated water in sufficient quantity was employed. As a result, complete visualization of the whole pancreas could be accomplished mainly from the gastric lumen via the gastric wall. Though the number of cases examined were still limited, ultrasonic differential diagnosis between benign and malignant lesions could be made much more clearly than those by currently used ultrasonic scanning.