Most patients with bleeding from the small bowel are frequently difficult to diagnose and treat because the rate of bleeding is slow and because this is the "blind area" of gastrointestinal endoscopy. We used a colonoscope passed by mouth intraoperatively in order to determine the site of bleeding in four patients. All patients required resection with one requiring laser therapy as well. We found that the following principles were important in maximizing the value of this technique: (1) Good communication between the endoscopist and operating surgeon during the procedure, (2) clamping the distal small bowel to prevent air accumulation in the colon (3) examining the bowel on the way in and avoiding the use of suction to minimize scope trauma artifact, (4) turning off the room lights in order to examine the transilluminated bowel externally, (5) examining the entire small bowel if possible, and (6) marking each site externally with a suture as it is identified.