The electrical activity of the colon was recorded during 10 hour sessions from 4 to 8 sets of electrodes carried on a 1.5 m probe in 11 control volunteers and in 35 patients with irritable bowel syndrome manifested by chronic constipation, diarrhea and/or pain. The patterns of electrical spiking activity were compared with that obtained from dogs with induced diarrhea or constipation. In both humans and dogs, two types of electrical activity were identified: short spike bursts (SSB) lasting 0.6 to 2.4 sec and long spike bursts (LSB) lasting 6.4 to 25 sec. The SSBs occurred at a maximum frequency of 13 per min. in man, while the LSB never exceeded 3 per min. Characteristic changes in the myoelectrical activity mainly coincided with disorders. In a group I containing 19 patients, most of them exhibiting constipation, the level of activity was 62% higher than in healthy subjects with an increase in the SSB hourly frequency of 170 to 420%. The colonic activity was similarly increased in constipated dogs. In a group II containing 11 patients suffering from soft feces or watery diarrhea, the LSB activity was significantly reduced. In a group III containing 5 patients, diffuse abdominal pain occurred after eating despite a reduction of the electromotor feeding responses and the absence of colonic postprandial rushes. The results indicate that the functional colonic disorders in man corresponded mainly to 3 specific patterns of myoelectrical activity, one of them (Group I) being reproduced in experimentally constipated dogs.