A 76-year-old female was diagnosed as having primary plasma cell leukemia (PCL), based on abundant atypical plasma cells in the circulation and bone marrow, monoclonalk light chain in the serum and urine, the immunophenotypeof the plasma cells and the lack of preceding multiple myeloma. The patient was treated with melphalan and prednisolone (MP), and complete remission (CR) was achieved; this was maintained for 28 months. The duration of CRin this patient appears to be the longest of those reported in well-documented primary PCL patients who have been treated with MPchemotherapy. (Internal Medicine 34: 251-254, 1995)