One hundred and nine distance runners participated in a questionnaire survey of bowel function related to running. Thirteen (12%) had had fecal incontinence while running. Sixty-eight (62%) had stopped to have a bowel movement while training. Forty-seven (43%) had "nervous" diarrhea before competition and 13 (12%) had stopped during competition for a bowel movement. Fifty-one (47%) had experienced diarrhea after racing or hard runs and 17 (16%) had seen blood in their stool in the same situations. Runners who had nervous diarrhea before competition were more likely to have symptoms of milk intolerance and irregular bowel function when not exercising, and runners who had symptoms of the irritable bowel syndrome often had to stop for a bowel movement during training. Runners with diarrhea after racing or hard runs frequently experienced severe abdominal cramps, nausea and vomiting, and occasionally, rectal bleeding at the same time. Any form of "runners' diarrhea" was unrelated to age, previous intestinal infection or food poisoning, food allergies, or dietary fiber.