The percentage of incorrect operations performed as a result of technetium-labeled erythrocyte scintigraphy has been reported as high as 42 per cent. Recent studies have found scintigraphy to be superior to angiography and propose that it be used as the primary diagnostic test in patients with lower gastrointestinal (GI) bleeding. A retrospective analysis was conducted of 105 patients with the symptoms of lower GI hemorrhage to determine the effect of erythrocyte scintigraphy on surgical management. Operative and pathology results were analyzed to determine the accuracy of the scintigraphy for localization of the bleeding source. In addition to tagged erythrocyte scans, 95 of 105 patients had additional diagnostic procedures: colonoscopy (78), upper endoscopy (47), and angiography (9). Scintigraphy localized a site of bleeding in 42 patients (colon, 29; jejunum/ileum, 10; duodenum, 2; esophagus, 1). Surgical intervention was required in 25 patients, and the site of bleeding was correctly determined by scintigraphy in 22 of these patients (88%). The scans were negative in two patients, and the bleeding site was incorrectly reported in another. The patients who had operations were significantly more likely to have positive scintigraphy than the nonoperative group (P < 0.05). Preoperative localization of GI hemorrhage is possible in most patients with technetium-labeled erythrocyte scans (88% of operative patients). When combined with other tests to exclude upper GI bleeding, scintigraphy is a reliable means of guiding surgical intervention.