To determine the effect of a standard meal on colonic myoelectrical and motor activity in the irritable-bowel syndrome and to determine the effect of a single dose of an oral anticholinergic drug (clidinium bromide) on this response, we studied 10 patients. These patients showed a prolonged increase in both colonic spike (P less than 0.05) and motor activity (P less than 0.05) after eating as compared to normal subjects. Clidinium did not affect the frequency of colonic slow waves or the basal colonic spike and motor activity. However, the anticholinergic reduced the prolonged postprandial colonic spike and motor response in the patients and also reduced the postprandial increase in colonic contractions at 3 cycles per minute (P less than 0.05). These studies indicate that patients with the irritable-bowel syndrome show an abnormally prolonged post-prandial increase in colonic spike and motor activity. An anticholinergic drug reduces the duration and the magnitude of this abnormal colonic response.