Though the pathophysiology of the irritable bowel syndrome (IBS) is commonly attributed to dysfunction of the large intestine, evidence exists to incriminate the small bowel. In order to further explore the role of the small bowel in IBS several stimuli were applied, in an attempt to unmask the dysmotility of the jejunum and ileum. These included infusions of cholecystokinin-octapeptide (CCK-OP), a high fat meal, neostigmine and balloon distension of the ileum. Three groups (n = 8) each of age and sex matched healthy volunteers were studied; patients with IBS complained of predominant constipation (n = 8) or diarrhoea (n = 8). Patients with IBS responded excessively to stimulation by CCK-OP, fatty meal, and ileal distension. In general patients with diarrhoea were more sensitive to stimuli than those with constipation. The ileum responded more to stimulation than the jejunum. As in the large bowel, stimuli appear to unmask intestinal dysmotility in patients with IBS. Motor abnormalities were often accompanied by abdominal symptoms, raising the possibility that dysfunction of the small bowel contributes to the symptoms of IBS.