An increased awareness of intestinal distention or contraction is implicated in the pathogenesis of the irritable bowel syndrome. This study aimed to test this hypothesis in 20 patients with the irritable bowel syndrome and 10 controls by relating the reporting of abdominal sensations to the occurrence of the duodenal phase 3 activity front of the migrating motor complex. During prolonged recordings of interdigestive small bowel motility, subjects were asked to report any episodes of abdominal sensation they experienced. Diurnally, the rate of occurrence of abdominal sensation was significantly greater in patients with the irritable bowel syndrome than in controls (P less than 0.001); such episodes were coincident with a duodenal activity front in 9 patients with the irritable bowel syndrome and in 1 control (P less than .05). Moreover, the rate of occurrence of episodes of sensation was greater (P less than 0.01) during diurnal phase 3 activity than during diurnal phase 2 activity. When episodes were coincident with duodenal phase 3 activity, these activity fronts were of significantly greater amplitude (irritable bowel syndrome: median, 23 mm Hg) than "noncoincident" activity fronts (median, 17 mm Hg; P less than 0.05) in both patients and controls. These data strongly suggest that certain physiological small bowel motor events, if of sufficient contraction amplitude, are able to be perceived by a greater proportion of irritable bowel syndrome patients and with greater frequency than by healthy subjects. The authors conclude that the threshold for perception of intestinal contraction is lower than normal in at least some patients with the irritable bowel syndrome.