Two hundred fifty bone marrow specimens, including twenty seven from hematologically normal patients, were examined hitologically. The Wright's and Brachet's stains were used. Plasma cells were rarely seen in the peripheral blood and bone marrow of normal individuals, but they were prominent constituents in some pathological states. A number significantly increased of plasma cells or mieloma cells were usually recognized in bone marrow from patients with plasmacytoma. These cells ranged from a very anaplastic immature form to closely resembling plasma cell. Even in the same patient, considerable pleomorphism often occured, and variation in cell size, number of nuclei and degree of nuclear immaturity were common. Although the results report certain observations regarding to the other cell series in patients with plasmacytoma. The most suggestive evidences were: 1. The red cells exhibited a tendency to agglutinate readily with "rouleaux" formation. 2. Increase in the number of metamyelocytes and segmented neutrophils with great variation in size and nuclear configuration. 3. Great increase in large platelet, atypical megakaryocyte forms and single, multiple or segmented naked nuclei. Details will be described elsewhere.