We examined the physiology of continence in 12 patients at least four months after colectomy, mucosal proctectomy, and endorectal ileo-anal anastomosis for ulcerative colitis and familial polyposis. The mean fecal output (+/-SEM) was 598 +/- 60 gm, passed as 12 +/- 4 movements/24 hr, of which 4 +/- 1 were passed at night. The patients were generally continent during the day and could distinguish gas from stool, but 11 of 12 leaked stools at night. Anal sphincter resting pressures (71 +/- 8 cm H2O) and squeeze pressures (171 +/- 15 cm H2O) of patients were similar to those of ten healthy controls (P greater than 0.05), although the rectal inhibitory reflex was absent in the patients. After operation, the distal bowel had a pressure-volume curve of greater slope (0.15 +/- 0.05 ml/cm H2O) than it had in controls (0.07 +/- 0.01 ml/cm H2O, P less than 0.05) and a lesser maximum capacity (patients, 248 +/- 31 ml; controls, 406 +/- 26 ml; P less than 0.05). The greater the capacity of the neorectum, the fewer was the number of bowel movements/day (r = 0.91, P less than 0.001). We concluded that the operation preserved the anal sphincter, although it decreased the capacity and compliance of the distal bowel and impaired continence.