In order to elucidate the effects of various antibiotics (carzinophilin, actinomycin C, chromomycin, mitomycin) and OX substance on the function of leukemic cells, the author performed clinical tissue culture of bone marrow of various leukemic patients. First the author performed bone marrow tissue culture of normal persons with addition of various antibiotics and OX substance in graded concentrations and established the maximal concentration of the agents in the medium, which does not impede the bone marrow cell growth. The author observed the effect of direct addition of various antibiotics and OX substance at this maximal concentration on the relative growth of the tissue, the wandering velocity of the cells, and the cell density in the bone-marrow tissue culture of various leukemic patients; and obtained the following results: 1. In acute myelogenous leukemia chromomycin and actinomycin C acted somewhat inhibitorily on the cell growth of the bone marrow. 2. In chronic myelogenous leukemia the inhibitory effect was found, though only slightly, to be in the descending order of carzinophilin, mitomycin, chromomycin and OX substance. 3. In acute lymphocytic leukemia and in chronic lymphocytic leukemia, no agents acted inhibitorily on the cell growth of the bone marrow. 4. In monocytic leukemia mitomycin showed an inhibitory effect to a moderate degree. 5. Judging from the effects of these drugs on leukemic cells, it may be expected that the efficacy of these drugs in the treatment of various leukemias is as follows: In actue myelogenous leukemia chromomycin is mildly effective; in chronic myelogenous leukemia carzinophilin is also mildly effective; and in monocytic leukemia mitomycin mildly effective.