Occult gastrointestinal bleeding was defined as continued bleeding in spite of a normal series of roentgenorgrams of the upper part of the gastrointestinal tract, barium enema, and sigmoidoscopy. Twenty-six such patients were treated. A thorough systematic evaluation, including gastroscopy, colonoscopy, visceral angiography, and isotopic scanning, was done preoperatively. Using colonoscopy and arteriography, nearly 60% of the bleeding sites were identified. Seventy-six percent of the lesions identified were in the terminal part of the ileum or the ascending colon. Exploratory laparotomy should be performed for life-threatening hemorrhage or as a diagnostic test only after a thorough preoperative evaluation. If results of a complete preoperative evaluation including arteriography were normal, then the likelihood of finding a discrete cause of bleeding at laparotomy was high (80%). A systematic evaluation and diligence of both physcian and patient in localizing the site of bleeding are essential.