This prospective trial in patients with left-sided ulcerative colitis evaluated the efficacy and acceptability of biweekly high-dose 5-aminosalicylic acid (5-ASA) enemas (4g/100ml) in maintaining a remission recently induced using daily 5-ASA enemas. Thirty-one patients were randomly assigned, 16 to 5-ASA and 15 to oral sulphasalazine (2g/day), and examined monthly. Sigmoidoscopy was performed "blind" at six months or at clinical relapse. Twelve patients on 5-ASA (75%) and nine on sulphasalazine (60%) remained in clinical and endoscopic remission throughout the study (NS), and the survival curve for 5-ASA was better at all points (NS). No patient stopped therapy due to side effects, and all those on 5-ASA chose to continue rectal maintenance therapy after the study. It was concluded that biweekly 5-ASA enemas is at least as effective as oral sulphasalazine in maintaining remission in unselected patients whose remission has been achieve using local therapy.