The distribution of pain from the colon was examined in normal subjects and in patients with irritable bowel syndrome (IBS). Colonic pain was induced by inflating a balloon (introduced during colonoscopy) at several sites throughout the colon. The pain was felt predominantly in the central, lower, and left abdomen in nine patients presenting with rectal bleeding and no spontaneous pain. Pain was felt in any part of the abdomen in 48 patients with painful IBS. Distension of the ascending and transverse colon often produced right-sided or upper abdominal pain in patients with IBS and in 29 of the 48 the pain induced was the same in quality and site as their presenting complaint. In addition pain was referred to several, previously undescribed, extra-abdominal sites. Wider recognition of the distribution of colonic pain could prevent unnecessary investigations including laparotomy.