Colonic electrical control activity and colonic motor activity in patients with IBS were compared to that found in patients who were equally psychologically disturbed but without bowel symptoms and to the colonic activity of normal subjects. A psychologic assessment was followed by measurement of activity in the rectosigmoid colon during baseline, a neutral interview, a stressful interview, and after a meal or neostigmine. Myoelectrical activity was recorded from two intraluminal bipolar suction electrodes; motor activity was recorded from two intraluminal strain gauges at the same sites. The number and duration of contractions per minute were determined by inspection of the motor activity record; the frequency content of both the motor and myoelectrical records was determined using the Fast Fourier Transform method. Patient selection was successful in producing two groups psychologically similar to each other and more disturbed than the normals. The IBS group had a greater number and duration of contractions than the normals at one recording site during baseline; there were no differences in electrical control (slow wave) activity between these same two groups. The IBS group did not differ significantly from the neurotic group on measures of either electrical control activity or motor activity. Possible reasons for the discrepancies between this and some previous studies are discussed.