Whole-gut transit time was measured by the time taken for an orally administered dose of brilliant blue dye to disappear from the stool in 20 patients with ulcerative proctitis and in 20 age- and sex-matched controls. Ten of the patients had active, and 10 inactive disease. The dye usually appeared in the stool with the next bowel movement after ingestion in both patients and controls; however, the time at which the dye disappeared from the stool (transit time) was prolonged to 76.1 h in the patients, compared with 50.2 h in the controls (p less than 0.01). This delay occurred both in patients with active disease at 70.5 h (p less than 0.05) and in those with inactive disease at 81.8 h (p less than 0.05). This prolongation of transit time may be relevant to both the pathogenesis and treatment of ulcerative proctitis.