Thirty consecutive patients had laboratory assessment of anorectal function after rectal excision and stapled coloanal anastomosis for rectal carcinoma. Eleven patients experienced perfect continence but 19 had faecal leakage with or without urgency of defaecation. Median (interquartile range) function was related to the pressures generated in the anal sphincter at rest (good versus poor function: 80 (63–91) versus 51 (23–60) cmH2O, P<0±01), during maximum squeeze (160 (126-203) versus 102 (58-112) cmH2O, P<0±01) and during reflex inhibition (58 (23-63) versus 36 (18-54) cmH2O, P<0±05). Poor function was significantly commoner in women than in men (P<0±01). These findings suggest that occult damage may have occurred to the anal sphincter before low anterior resection. Careful preoperative evaluation with manometry and endoanal ultrasonography may detect such damage and allow selection of patients for colopouch reconstruction.