This study was designed to investigate whether rectal compliance is altered in females with obstructed defecation.Eighty female patients with obstructed defecation and 60 control subjects were studied. Rectal compliance was measured with an "infinitely compliant" polyethylene bag. This bag was inserted in the rectum and inflated with air to selected pressure plateaus (range, 0-60 mmHg; cumulative steps of 2 mmHg with a duration of ten seconds) using a computer-controlled electromechanical barostat system. Volume changes at the levels of distending pressures were recorded. The distending pressures, needed to evoke first sensation of content in the rectum, earliest urge to defecate, and the maximum tolerable volume were noted.In all cases, the compliance curve had a characteristic triphasic (S-shaped) form. The mean compliance curve obtained from the patients was identical to that of the controls. However, the course of the compliance curve fell above the normal range (mean + 2 SD) in 14 patients. In ten (71 percent) of these patients, a large rectocele was seen at evacuation proctography. Such a rectocele was observed in only five patients (7.6 percent) with a normal compliance curve (P < 0.001). Eighty percent of the controls experienced earliest urge to defecate during the second phase of the curve. In 75 percent of the patients, this occurred in the third phase. The mean pressure threshold for first sensation, earliest urge to defecate, and maximum tolerable volume were significantly higher in patients compared with control subjects. Ten of the patients experienced no sensation at all in the pressure range between 0 and 60 mmHg.In females with obstructed defecation, the compliance of the rectal wall is normal.