Treatment of severe, chronic idiopathic thrombocytopenic purpura (ITP) refractory to most usual therapies is a difficult challenge. Little information exists on the clinical use of cyclosporin A (CyA) in the treatment of ITP. This report describes long-term treatment with CyA (median, 40 months) and follow-up (median, 36.8 months) in 12 adult patients with resistant ITP. CyA used in relatively low doses (2.5-3 mg/kg of body weight per day) led to a clinical improvement in 10 patients (83.3%). Five had a complete response (41.1%), 4 a complete response to maintenance therapy (33.3%), and one a partial response (8.3%). Two patients had no response. Most patients with a response (60%) had a long-term remission (mean, 28.6 months) after discontinuation of CyA. One patient had a relapse of ITP 4 years after CyA therapy was stopped. Side effects were moderate and transient, even in patients dependent on continued CyA treatment. CyA seems to represent reasonable salvage treatment in severe, potentially life-threatening, refractory ITP.