Conventional transcutaneous ultrasound examinations are often compromised by intervening pulmonary or bowel gas and have limited resolution. Ultrasonic probes of frequencies greater than 5 MHz, which enhance resolution, cannot be used successfully on the skin surface, because they do not penetrate deeply enough to view intraabdominal organs in most adults. To overcome these problems, we tested an ultrasonic endoscope which had a 10-MHz, 64-element linear assay, generated real-time images at resolutions of less than 1 mm, and was an integral part of a 35-mm-long and 13-mm-wide endoscopic rigid tip. Thirty-two studies were performed in 15 healthy subjects, 4 patients with pancreatic cancer and 6 patients with chronic pancreatitis, and 1 patient each with a gastric ulcer and a suspected pancreatic abscess. We demonstrated that this procedure is safe, provides high resolution real-time ultrasound visualization of the heart, aorta, spleen, pancreas, liver, gallbladder, kidneys, and gastrointestinal mucosa and can detect moderate-sized pancreatic tumors and hepatic metastases less than 1 cm in diameter. Because endoscopic visualization of gastrointestinal mucosa and ultrasound examination of extraluminal organs can be obtained during a single procedure, rapid differentiation among mucosal and intramural disease of the hollow gut and disease of extraluminal organs should be possible with this diagnostic technique.