Sixty-eight patients with massive lower gastrointestinal (G.I.) hemorrhage underwent emergency arteriography. Patients were transfused an average of six units of packed red blood cells within 24 hours of admission. The bleeding source was localized arteriographically in 27 (40%), with a sensitivity of 65% among patients requiring emergency resection. However, twelve of the 41 patients with a negative arteriogram still required emergency intestinal resection for continued hemorrhage. Radionuclide bleeding scans had a sensitivity of 86%. The right colon was the most common site of bleeding (35%). Diverticulosis and arteriovenous malformation were the most common etiologies. Selective intra-arterial infusion of vasopressin and embolization were successful in 36% of cases in which they were employed and contributed to fatality in two patients. Twenty-three patients underwent segmental resection, whereas seven patients required subtotal colectomy for multiple bleeding sites or negative studies in the face continued hemorrhage. Intraoperative infusion of methylene blue via angiographic catheters allowed successful localization and resection of bleeding small bowel segments in three patients. Overall mortality was 21%. The mortality for patients without a malignancy, with a positive preoperative arteriogram, and emergency segmental resection was 13%.