Anorectal function in ulcerative colitis was assessed by measuring pressures at multiple sites in the anus and rectum under basal conditions and during balloon distention of the rectum in 29 patients with ulcerative colitis (12 active, 11 quiescent, and 6 during both phases) and in 12 normal controls. Resting and squeeze sphincter pressures were similar in the three groups. The lowest rectal volume that could be perceived, the volume required to induce a desire to defecate, and the maximum tolerable rectal volume were all lower in patients with active colitis than in patients with quiescent colitis (p less than 0.001) and controls (p less than 0.001). The rectal volume required to cause a sustained anal relaxation was lower in patients with active colitis (p less than 0.05) than in controls. Both peak and steady state rectal pressures in response to rectal distention were significantly higher in patients with active colitis than in patients with quiescent colitis (p less than 0.05) and controls (p less than 0.02). Paired studies showed that during remission of disease there was a decrease in rectal sensitivity (p less than 0.05) and an increase in rectal compliance (p less than 0.05). These results suggest that the frequent and urgent defecation, i.e., the predominant feature of active colitis, is related to a hypersensitive and poorly compliant rectum, which, upon distention, is more reactive and is more likely to induce prolonged sphincter relaxation.