Endoscopic ultrasound examination (EUS) of the upper gastrointestinal (GI) tract for the assessment of mural and extramural pathology has attracted growing international interest in recent years. Since February 1989, EUS has been performed on selected patients in our institution using a new Picker-Pentax fiber-optic ultrasound (US) gastroscope. The instrument consists of a forward-view fiber-optic gastroscope with a 5-MHz curved-array linear US transducer mounted directly behind the lens. The scanning plane lies in the long axis of the scope. Based on in vitro US examinations and EUS of 118 patients over an 18-month period, our preliminary experience with the instrument is described. Using EUS, various lesions in the esophageal wall as well as in the gastric and duodenal walls can be visualized. Furthermore, organs and structures outside the GI tract can be seen, and lesions such as enlarged lymph nodes in the mediastinum and abdomen; solid and cystic masses in the liver, pancreas and retroperitoneum; arterial aneurysms; esophageal varices; and gall stones and calcifications can be demonstrated. The 5-MHz transducer does not provide very detailed information on the GI wall. The direction of the ultrasound scanning planes is difficult to define, as the transducer cannot be seen through the optic lens. The method demands great expertise in endoscopy and ultrasound. Indications for EUS have not been definitively established. Evaluation of the diagnostic accuracy of this technique requires further controlled studies. We believe that EUS using a curved-array linear transducer will provide significant diagnostic information of clinical relevance to gastroenterology.