The effect of chemotherapy on dysplasia of bone marrow cells was studied in 10 patients with hypoplastic leukemia. Patients were all previously untreated, and ages ranged from 40 to 81 years old (median : 70). Male to female ratio was 1 : 1. Morphologic features studied were pseudo-Pelger neutrophils, absence or decreased Azur granules in the neutrophilis, multinu-cleated erythroblasts, megaloblastoid changes in erythroblasts, micromegakaryocytes, mononuclear megakaryoctes and megekaryocytes with multiple small separated nulei. Although 8 patients with chemotherapeutic effect showed little evidence of dysplasia, 2 patients without chemotherapeutic effect showed severe dysplasia in two or three blood cell lineages. These findings sre thought to indicate that a part of hypoplastic leukemia develops from myelodysplasia with hypoplastic marrow. The establishment of an optimal treatment for hypoplastic leukemia should be sytudied by stratification of bone marrow dysplasia.