In a series of 500 patients undergoing emergency endoscopic examination to detect the source(s) for upper gastrointestinal bleeding, the examination failed in its purpose in 55 cases (11%). This group was analyzed. Thiry-seven of these individuals demonstrated large and extensive esophagogastric varices which, while not observed to bleed during the examination, represented a potential bleeding source of great significance. The clinical implication of this endoscopic finding is described. Variceal bleeding frequently recurs sporadically, ceases abruptly and leaves no visible evidence of the point of rupture. Lacking this latter factor, the endoscopist is usually reluctant to assign responsibility for bleeding to these lesions. When, however, large varices are discovered as the sole potential source for bleeding, they may be assumed, with good reason, to represent the actual source and specific treatment logically may be instituted.