We describe a case of neutrophil aplasia in a woman with recurrent myasthenia gravis and a past history of thymoma. Bone marrow showed virtually absent granulopoiesis but normal erythropoiesis and megakaryopoiesis. Bone marrow cultures showed no growth of granulocyte/mononuclear cell progenitors (CFU-GM). She was treated with immunosuppression including azathioprine, and her neutrophil count returned to normal. Serum before treatment, and also an IgG fraction thereof, inhibited CFU-GM growth both in autologous 'remission' marrow and in allogeneic marrow. She remains in complete remission 36 months after starting azathioprine. This association is extremely rare, and was formerly associated with a grim prognosis.