Effects of an artificial mental stress on colonic motility, autonomic nervous system, and gastrointestinal hormones were examined in patients with irritable bowel syndrome (IBS). The subjects were 20 patients with typical IBS and 12 controls. A transducer was inserted to the sigmoid colon from the anus for measuring colonic intraluminal pressure, and mirror drawing test was loaded as psychological stress. At the same time, coefficient of variation of R-R interval on ECG (CV-RR) was measured and the levels of plasma catecholamines, gastrin, glucagon, and motilin were assessed. Colonic motility showed a significant increase in the IBS patients during the stress compared with that in controls (p less than 0.01). Motilin also increased significantly in the IBS patients after the stress (p less than 0.01). CV-RR and motilin revealed positive relationship with colonic motility alteration in the IBS patients although no significant change was detected in controls. These phenomena are thought to be due to autonomic nervous dysfunction and/or gastrointestinal hormonal derrangments induced by psychological stress. It is suggested that organ specificity of the alimentary tract for the stress exists in this disease.