6 patients with pure red-cell aplasia were treated with Ciclosporin (Cyclosporine A; CS) alone or combined with prednisolone for a period of 9-46 (median 27) months. Prior to study, 5 cases had refractory disease, steroids were contraindicated in 1, and 4/6 patients, including 2 cases with congenital disease, had a disease duration exceeding 11 years. A complete haematological response was obtained in 5/6 subjects, and a partial response in 1. When the pre-treatment Hb levels (mean +/- S.D. = 64 +/- 13 g/l, range 41-80) for all 6 PRCA patients were compared with the Hb levels after 6 months of CS therapy (104 +/- 17 g/l, 80-125), a significant improvement was registered (p less than 0.005). In half of the patients, remission is maintained with CS as single drug in a dose-dependent manner. We also treated 5 patients with refractory severe aplastic anaemia with CS (1 case) or CS plus prednisolone (4 cases) for 3-27 (median 10) months. Only 1 patient responded. In this case, a complete haematological remission was induced with CS alone, and remission has been maintained for 27 months. Side effects of CS therapy were common but were dose-dependent and reversible, with the exception of persistent nephrotoxicity in 1 patient with pure red-cell aplasia. Based on our present results and a survey of the literature, we conclude that CS therapy is effective and indicated in refractory pure red-cell aplasia. In severe aplastic anaemia resistant to conventional immunosuppression, the response rate is lower, but a small proportion (around 15%) of patients may benefit from CS therapy. Longer treatment periods may, however, be needed to evaluate the role of CS in aplastic anaemia.