Colon motility and myoelectric slow wave activity were compared in 10 patients with progressive systemic sclerosis and 18 controls. Recordings were made in the rectosigmoid and rectum, 25-30 cm and 10-15 cm from the anal margin, respectively, during two 4-min baselines and in response to stepwise distention of the colon with an air-filled balloon. During baseline, the motility (activity index, defined as cumulated areas of all waves divided by recording time) of the rectosigmoid was similar in patients with progressive systemic sclerosis (0.38 +/- 0.61 in baseline 1, 0.86 +/- 1.33 in baseline 2) and controls (1.15 +/- 2.02 in baseline 1, 0.77 +/- 1.01 in baseline 2). Rectal motility was also similar during baseline in patients with progressive systemic sclerosis (1.43 +/- 2.56 in baseline 1, 1.65 +/- 2.47 in baseline 2) and controls (0.56 +/- 0.80 in baseline 1, 0.62 +/- 0.94 in baseline 2). Patients showed a lower tolerance for balloon distention of the colon (average, 130 vs. 184 ml) and a greater amount of contractile activity than controls after balloon distention (rectosigmoid activity index, 1.05 +/- 1.24 vs. 0.07 +/- 0.14; rectal activity index, 2.75 +/- 3.71 vs. 0.13 +/- 0.31). Maximum tolerable volume of balloon distention was inversely correlated to complaints of diarrhea in patients. Slow wave myoelectric activity did not differentiate patients from controls. These findings suggest that diarrhea, and possibly other gastrointestinal symptoms associated with progressive systemic sclerosis, may be due to decreased compliance of the bowel.