The cases of three patients who had clinical courses and hematologic data consistent with plasma-cell leukemia or a terminal leukemic phase of multiple myeloma are presented. A double Bence Jones protein was demonstrated in the urine of two of the patients. Immunoelectrophoresis and immunofluorescence studies demonstrated kappa light chains. In serum and urine of the third patient, no immunoglobulin abnormality was demonstrated. The three patients had rapidly fatal courses unresponsive to treatment.