A multicenter prospective study was carried out to evaluate the efficacy of cyclosporin A (CsA) in 32 patients with myelodysplastic syndromes. The FAB subtypes of the patients included refractory anemia, refractory anemia with ringed sideroblasts, and refractory anemia with excess blasts. The dosage of CsA was 3 to 6 mg/kg per day and was adjusted according to the blood concentration of CsA and the responses of patients. The drug was administered twice a day for more than 3 months. After 3 months of treatment, hematological improvement was observed in 18 of 32 patients (56.3%) by the criteria of the International Working Group. At the end of the follow-up (median time, 14 months), 4 patients showed alteration of disease progression, including 1 complete remission and 3 partial remissions, and 16 patients showed hematological improvement. There were a total of 20 responders. The response rate was 62.5% (20/32). It was shown that the CsA therapy was effective in patients with refractory anemia or refractory anemia with excess blasts and both hypo- and hyperplastic bone marrows might respond to the therapy. The survival time was significantly longer in responders than in nonresponders. The study shows that CsA therapy is potentially the most effective therapy for myelodysplastic syndromes.