The treatment of autoimmune thrombocytopenic purpura (AITP) remains unsatisfactory in patients refractory to first-line management such as corticosteroid therapy and/or splenectomy. Patients with refractory AITP usually require unacceptably high doses of corticosteroids to maintain a safe platelet count. Immunosuppressive treatment with cyclosporin A (CsA) is a relatively new treatment modality, and no large studies of this drug have been conducted. We used CsA in 6 patients with refractory AITP who had platelet counts of less than 20 x 10(9)/L without any therapy or who had evidence of subcutaneous and mucosal bleeding. All 6 patients had undergone splenectomy. When CsA therapy was begun, 5 of the patients were receiving methylprednisolone (MP) at a daily dose of 32 mg or greater. During the following months, the MP dosage was tapered, or the drug was withdrawn. Three patients achieved a complete remission (CR), whereupon CsA treatment was gradually discontinued. Two of these 3 patients later relapsed, but both responded to an additional course of CsA and achieved a second CR. The remaining 3 patients achieved a partial remission (PR). One patient, a woman with an AITP history of more than 30 years, obtained a stable PR with a platelet count substantially greater than 20 x 10(9)/L, which was successfully maintained by low doses of CsA and MP. The most frequent side effect of CsA therapy in our patients was a painful edema of the lower extremities. Our experience shows that CsA is a safe and effective treatment option for patients with refractory (chronic) AITP. It may be given at a low dose as maintenance therapy, and remissions may be sustained even after the drug has been discontinued.