Four cases of plasma cell leukemia are reported. Hematologic, immunologic and biochemical data of the patients were analyzed with the special attention to the diagnostic problems. They showed 42%, 28%, 8% and 31% of plasma cells in peripheral blood, and 97%, 78%, 98% and 92% in none marrow, which were enough for diagnostic criteria of plasma cell leukemia. Their abnormal proteins on serum protein electrophoresis were found on gamma globulin fraction in three and on beta globulin fraction in one of them, and immunoelectrophoresis performed on three of them revealed IgG-Kappa, IgG-lambda and IgA lambda in each patients.