About eighty percent of patients with severe ulcerative colitis refractory to steroids are responsive to intravenous cyclosporine therapy within a few days. However, no controlled data are available on intravenous cyclosporine therapy in steroid refractory Crohn's disease. In this study 7 patients with severe ulcerative colitis and 4 patients with active Crohn's disease unresponsive to prednisone were treated with high dose intravenous cyclosporine. A response was estimated by a decrease of Crohn's disease activity index (Best) and colitis activity index (Rachmilewitz). Six of 7 patients with ulcerative colitis showed a significant decrease in colitis activity index (index before therapy: 15 +/- 2; one week later: 7 +/- 1; p < 0.001). In these patients prednisone could be tapered to a dose less than 20 mg/day within 6 months during oral cyclosporine and concomitant azathioprine therapy. Cyclosporine medication was withdrawn within a few weeks and the clinical response could be preserved for another 6 months. In 3 of 4 patients with Crohn's disease intravenous cyclosporine led to a temporary improvement of the Crohn's disease activity index (before treatment: 343 +/- 43, after one week: 194 +/- 20; p < 0.05). Nevertheless, all of these patients had an early relapse under oral cyclosporine therapy. Our data confirm the efficacy of intravenous cyclosporine as a rapid acting drug for severe ulcerative colitis. Maintenance therapy with azathioprine preserved the clinical response for one year. In patients with steroid refractory Crohn's disease intravenous cyclosporine showed only a short term effect.