The mainstay of therapy for pyoderma gangrenosum has been corticosteroids, but many patients respond poorly. During the past 2 years we have treated seven patients who had pyoderma gangrenosum with cyclosporine after their condition proved resistant to conventional therapy. No evidence of permanent toxicity from cyclosporine was detected and treatment with other immunosuppressive agents was discontinued in five of seven cases. Tuberculosis was reactivated in one patient. Three patients had a remission, three had an intermediate response, and one did not respond. These results indicate that cyclosporine is useful in the treatment of patients with refractory pyoderma gangrenosum and suggest an immune mechanism in the pathogenesis of this disorder.