A 64 year old man admitted to hospital with increasing effort dyspnoea and lethargy was found to have a thymoma and pure red cell aplasia. Lymphocytes accounted for 20-30% of marrow cells, and numbers of T8 suppressor/cytotoxic cells in peripheral blood were greatly increased. He remained anaemic after removal of the thymoma despite blood transfusions, and immunosuppression with prednisolone 60 mg and cyclophosphamide 50 mg daily was started. The dose of prednisolone was reduced to 15 mg owing to steroid myopathy and the risk of opportunistic infection. He went into remission, and the dose was further decreased to 10 mg daily.