BACKGROUND & AIMS: Cyclosporine has been effective in patients with steroid-refractory attacks of ulcerative colitis (UC). We investigated the effects of intravenous (IV) cyclosporine as single IV therapy (without glucocorticosteroids) for severe UC and compared these with the response to glucocorticosteroids. METHODS: Patients with a severe attack of UC were randomized to treatment with IV cyclosporine, 4 mg x kg(-1) x day(-1), or with methylprednisolone, 40 mg/day, in a randomized, double-blind, controlled trial. After 8 days, patients who had a response received the same medication orally in combination with azathioprine. Patients were followed up clinically, endoscopically, and by scintigraphy. Renal function was assessed using urinary inulin clearances. Endpoints were clinical improvement, discharge from the hospital, and remission up to 12 months after intravenous therapy. RESULTS: Thirty patients were included. After 8 days, 8 of 15 patients (53%) who received methylprednisolone had a response to therapy vs. 9 of 14 (64%) receiving cyclosporine. In nonresponders, 3 of 7 methylprednisolone patients and 1 of 3 cyclosporine patients improved when both treatments were combined. No serious drug-related toxicity was observed with either treatment. At 12 months, 7 of 9 patients (78%) initially controlled with cyclosporine maintained their remission vs. 3 of 8 (37%) initially treated with methylprednisolone. No clinically significant decrease of renal function was observed. CONCLUSIONS: Cyclosporine monotherapy is an effective and safe alternative to glucocorticosteroids in patients with severe attacks of UC.