The blood cells in the bone marrow of leukemia before and after antileukemic chemotherapy and those of hypoplastic anemia were observed morphologically by vital staining. 1. In acute myelogenous leukemia at remission, the mitochondria of the atypical promyelocytes displayed variation in size and those of the lymphocytes and the erythroblasts showed the same change. Some of neutral red granules of the young neutrophilic cells became larger in size. 2. In acute lymphocytic leuklemia at remission, the mitochondria of the lymphoblasts and the atypical lymphocytes exhibited a considerable variation in size and during the tissue culture, some of those mitochondria developed small vacuoles. 3. In monocytic leukemia at remission, the mitochondria of the promonocytes displayed a slight variation in size. 4. In chronic myelogenous at remission, the mitochondria of the young neutrophilic blood cells became varying in size and many neutral red vacuoles appeared in the cytoplasm of mature neutrophils. Appearance of many unstainable vacuoles around the nucleus of the myelocytes seemed to be characteristic in the chronic myelogenous leukemia at remission that showed the hypolastic pattern in bone marrow tissue culture. 5. In hypoplastic anemia, unstainable vacuoles which were observed in treated chronic mylogenous leukemia made no appearance. In conclusion, the morphologic changes observed after treatment were considered to be the pictures of cellular degeneration that were superimposed over the cytologic characteristics of leukemic cells and accordingly, by this feature leukemia was able to be cytologically diagnosed even at remission.