When properly employed, endoscopic examination of the upper gastrointestinal tract with the flexible maneuverable-tip fiberoptic instruments is the most accurate method of diagnosing any upper gastrointestinal tract disease. Two hundred consecutive endoscopic procedures in the upper gastrointestinal tract were performed without significant morbidity or mortality; the results were reviewed to ascertain the overall diagnostic value of this modality. Although the overall numbers in each subgroup are still small, the experience indicates that: (1) thorough endoscopic examination of the upper gastrointestinal tract can be carried out expeditiously in most patients without morbidity; (2) upper gastrointestinal tract disease can be precisely defined in the majority of patients; and (3) endoscopic examination frequently alters the initial clinical diagnosis. The precise cause of upper gastrointestinal tract hemorrhage can be diagnosed in at least three of four cases. Some unnecessary operations can be avoided and proper therapy for specific sources of bleeding can be initiated promptly.