Three patients (1 PRCA-T-CLL, 1 PRCA-B-CLL, 1 B-CLL aplasia) were treated with cyclosporin A (CS-A). Patient no 1 had relapsed during steroid therapy and the remaining two patients had been resistant to conventional immunosuppression. CS-A produced in all cases a prompt remission (within 1-4 weeks) of bone marrow failure. Mild reversible renal toxicity was the only side-effect noted. CS-A might be tried in every case of CLL-associated bone marrow failure.