Although the irritable bowel syndrome has been characterized as an abnormality in colonic motor activity occurring in response to certain stimuli, the etiology of this abnormality is unclear. The purpose of this study was to compare colonic myoelectric and motor activity in normal subjects and in patients with the irritable bowel syndrome. Myoelectric activity was recorded using a bipolar electrode clipped to the mucosa of the rectal and rectosigmoid areas. Basic electrical rhythm (BER), spike potential activity, and intraluminal pressure were recorded in both groups. Two types of BER were observed. The major component of the BER had a frequency of approximately 6 cycles per min, whereas the minor component had a frequency of approximately 3 cycles per min. Although both types of BER were recorded in the two groups, thitable bowel syndrome. The 3 cycles per min activity was present as 44.1 +/- 1.3% of the total BER in the irritable bowel syndrome, as compared with 10.0 +/- 1.6% in the normal group (P less than 0.001). Basal spike potential and motor activity were similiar in both groups. Because it had been demonstrated previously that colonic responsiveness to certain stimuli was increased during the slower frequency BER, it is suggested that the abnormalities in colonic motor response reported in the irritable bowel syndrome may be related to this difference in colonic BER.