Antithymocyte globulin (ATG) is an established form of therapy for severe aplastic anemia (SAA). However, in patients who do not respond to this treatment and who are not candidates for bone marrow transplantation few successful therapeutic alternatives exist. We report two such patients who have shown a therapeutic response to Cyclosporin A (CSA) (Sandimmune, Sandoz). Case 1, a 15 year old male, and Case 2, a 34 year old female, were diagnosed as having SAA in September 1984 and May 1984 respectively. Treatment with high dose Methylprednisolone (MPN) and ATG in Case 1 and MPN, ATG and Oxymetholone in Case 2 for ten days was ineffective in both cases. Case 1 developed anaphylaxis with both repeat ATG and ALG (antilymphoblast globulin), and Case 2 failed to respond to repeat ATG. Both required frequent packed cells and platelet transfusions. At five and six months respectively following completion of ATG therapy, CSA was started at 10 mg/kg/day in divided doses orally. Renal and liver functions and CSA blood levels were followed. Within six weeks both patients exhibited a hematologic response and were no longer transfusion dependent. On maintenance therapy of 4 mg/kg/day (Case 1) and four months after discontinuing CSA (Case 2) the hematologic values are as follows: hemoglobin 160 and 130 g/L, absolute granulocyte count 3100 and 1640 X 10(9)/L, and platelets 132 and 84 X 10(9)/L respectively. Side effects included hypertrichosis, gingival hyperplasia and mild reversible nephrotoxicity. CSA appears to represent an effective form of therapy for patients with SAA refractory to ATG.