The hypothesis that anal sensation might be better after restorative proctocolectomy with end-to-end ileoanal anastomosis than after mucosal proctectomy with endo-anal anastomosis was tested in this study. Anal sensation was measured in 14 patients before operation, 16 patients after restorative proctocolectomy with end-to-end anastomosis (RP + EEA) and 13 patients after mucosal proctectomy with endo-anal anastomosis 1 cm above the dentate line (MP + EAA). Threshold electrosensitivity was measured in the upper, mid and lower anal canal by means of a bipolar constant current stimulator probe. The 'recto'-anal inhibitory reflex was tested, and the patients' ability to discriminate between flatus and faeces and to release flatus 'safely' was assessed by interview. In the upper anal canal, threshold sensitivity was significantly greater in patients who had undergone MP + EAA than in patients who had undergone RP + EEA (P less than 0.05). In the mid and lower anal canal, electrosensitivity in the three groups of patients did not differ significantly. Twelve patients (75 per cent) regained the 'recto'-anal reflex after RP + EEA, but after MP + EAA only three patients (23 per cent) did so (P less than 0.02). Thirteen patients after RP + EEA could release flatus safely without fear of faecal leakage, compared with only four after MP + EAA (P less than 0.02). The proportions of patients in these two groups who said they were able to discriminate flatus from faeces did not differ significantly. Anal sensation and discriminatory function are significantly better after end-to-end ileoanal anastomosis than after mucosal proctectomy with endo-anal anastomosis.