We report a case of pure red cell aplasia (PRCA) with benign monoclonal gammopathy (BMG) of IgA.lambda type and type I von Willebrand disease (vWD). A 61-year-old female patient was treated initially with prednisolone, azathioprine and cyclophosphamide with transient and unsatisfactory reticulocyte response. Oral administration of 200 mg of cyclosporine A (CyA)/day was started from July, 1987. A rapid and marked reticulocytosis was seen from a week later and there was a rapid increase in hemoglobin levels, and remission has been maintained for over 22 months. Patient's serum and IgA taken on admission did not show inhibitory activity to both CFU-E growth from her own bone marrow cells obtained in remission and von Willebrand factor. T cell-mediated suppression to CFU-E growth was detected. On family study, the patient's second son was found to be a type I vWD. These results indicate that there is no direct causal relationships between BMG and PRCA or vWD, and that CyA may have a place in the management of PRCA.