Twenty-one consecutive patients (10 male and 11 female) with ulcerative colitis who underwent colectomy, mucosal proctectomy, and endorectal ileal pullthrough with ileal reservoir were examined by serial anorectal sphincter measurements. Values were recorded before operation, after operation, and on two occasions during a 6-month period after ileostomy closure. Anal sphincter pressures and rectal ampullary volume measurements were performed using a new, simplified recording instrument. The anal resting pressure was elevated for both male and female patients preoperatively but decreased to levels slightly below normal control values after the pullthrough procedure. The maximal squeeze pressure was markedly elevated for both male and female patients preoperatively but decreased to levels near normal controls postoperation and remained at this level during the entire period of study. The rectal sensitivity threshold and rectal volume tolerance were markedly decreased preoperatively and appeared to correlate closely with the severity of inflammatory disease in the rectum. After the operation the maximal tolerance volume increased in direct relation with enlargement of the ileal reservoir and was associated with a slight, but definite, decrease in stool frequency. This study confirms the view that although mucosal proctectomy may have mildly adverse effects on anal sphincter function, this impairment is well compensated in most patients. Abnormalities recorded preoperatively are likely to persist after the pullthrough procedure. More than 90% of patients consider themselves continent after long-term follow-up evaluation.