Endoscopic ultrasound is a new technique in which high-frequency, high-resolution real-time ultrasound images are obtained from within the gastrointestinal tract by use of an ultrasound probe incorporated into the tip of a fibreoptic endoscope. Forty patients were scanned for gastrointestinal indications. In six patients the scans were technically unsuccessful, in three of these because of difficulties with the prototype instrument. New information was obtained in 20 patients, later confirmed by other means in 12. Endoscopic ultrasound did not provide any new information in 14 patients. The technique shows considerable promise in patients with pancreatic disorders and gut-wall malignancies. It has the ability to provide images with a spatial resolution unobtainable by other imaging methods.