Sixty-two patients with ulcerative colitis localised to the distal sigmoid colon and rectum (less than 20 cm) entered the trial. Thirty-two were treated with 5-ASA 500 mg suppositories (Asacol) 3 times a day for 1 month while 30 received a placebo given in the same regime. Clinical, sigmoidoscopic and histological assessment was carried out before, after 15 days and after 1 month of treatment. At the end of the study 5-ASA suppositories showed significantly better results in all the parameters recorded than placebo (p less than 0.01). There were no unwanted effects related to the use of suppositories. This treatment should therefore be offered as a first choice for patients with distal rectosigmoiditis.