Therapeutic efficacy of mesalazine controlled-release suppository 1 g once daily was compared with that of a placebo during 2 weeks in 50 patients (26 in the mesalazine group, 24 in the placebo group) with ulcerative proctitis, in a double-blind randomized trial. Endoscopic and clinical remission was seen in 69 and 65% of mesalazine-treated patients and in 33 and 25% of placebo-treated patients respectively (P < or = 0.01). No side effects were seen. It is concluded that a once-a-day administration of 1 g mesalazine controlled-release suppository is effective for topical treatment of patients with ulcerative proctitis.