A retrospective study of 35 patients with ulcerative colitis is presented. The patients were treated with Imuran, alone or combined with corticosteroids, in single or repeated courses, over a period of 11 years. The usual indication for Imuran treatment was nonresponse to Azulfidine or corticosteroids. Criteria for response to treatment were: 1. decrease in stool frequency, 2. decrease in frequency and amount of rectal bleeding and 3. weight gain. Improvement was noted on the average two weeks after the start of Imuran therapy and 62% of the patients had complete remission afer 1.7 months. When patient-months of remission and activity were compared on different therapies. Imuran, both alone and combined with steroids, was clearly superior to nontreatment or steroid therapy. With the exception of two patients with fulminant disease, who developed fatal septicemia on Imuran therapy, there were no serious complications. Seven patients eventually underwent colectomy and one patient developed carcinoma of the colon. Our results indicate that there is a definite place for Imuran in the treatment of selected patients with ulcerative colitis.