Treatment of acute attacks of ulcerative colitis in 89 patients with doses of prednisolone above or equal to 40 mg resulted in an overall remission in 67%. Remission rate and colectomy rate were 47% and 42%, respectively, when the disease was severe, 80% and 13% when moderate, and 84% and 3% when mild. The need for surgery was 28% in pancolitis, 11% in left-sided colitis, and 5% in proctitis. After subsequent treatment episodes colectomy was performed in 35% of patients with pancolitis, in 37% with left-sided colitis, and in 5% with proctitis. The median total duration of therapy in patients who went into clinical remission was 4 months, and the median dose just above 3 g prednisolone. Patients who stayed in remission during the follow-up received a significantly higher start dose and total dose of prednisolone in the treatment episode than patients who had a relapse. In 25 patients treatment with doses equal to or above 75 mg of prednisolone was continued beyond 10 days, and 11 patients experienced remission whereas 14 patients had surgery performed. Orally administered corticosteroids produce results comparable to those obtained after the previously suggested intravenous regimen.