One hundred fifty consecutive admissions to a metropolitan hospital center for upper gastrointestinal hemorrhage, were evaluated by emergency esophagoscopy and gastroscopy in a prospective study of the etiology of bleeding episodes. In 81 instances, the diagnosis was established by endoscopy alone—45 by gastroscopy and 36 by esophagoscopy. An acute gastric lesion (acute erosive gastritis or acute gastric ulcer) was the bleeding source 39 times, duodenal ulcer 29 times, esophageal varices 28 times, and chronic gastric ulcer 6 times, while 28 episodes remained undiagnosed. Chronic peptic ulcer (duodenal chronic gastric and marginal) was the bleeding source 37 times. Massive bleeding was established by three different criteria. In all three groups esophageal varices were the leading source of bleeding. Chronic peptic ulcer never exceeded 33.3% of any of the massive bleeding groups—nor did duodenal ulcer alone exceed 25.8%.