With the purpose clarify the effects of urethane and various alkylating agents(nitromin, myleran, colcemid, tespamin) of 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 urethane and various alkylating agents in graded concentrations and established the maximal concentration of the agents in the medium, which does not impede bone-marrow cell growth. At this maximal concentration the observation was carried on to see the effect of direct addition of urethane and various alkylating agents on the relative growth of the tissue, the wandering velocity of the cells, and the cell density by performing bone-marrow tissue culture of various Ieukemic patients; and obtained the following results: 1. In acute myelogenous leukemia the inhibitory effect on the bone-marrow cell growth was found to be in the descending order of nitromin, myleran, urethane, colcemid, and tespamin, and it was greatest with nitromin. 2. In chronic myelogenous leukemia the inhibitory effect was found to be in the descending order of nitromin, myleran, urethane, colcemid and tepsamin, and it was marked with nitromin and myleran. 3. In acute lymphocytic leukemia nitromin acted inhibitorily slightly, but other anti-leukemic agents had hardly any inhibitory action. 4. In chronic lymphocytic leukemia the inhibitory effect was found to be in the descending order of tepsamin, urethane, colcemid, nitromin and myleran; among them tespamin and urethane were more effective. 5. In monocytic leukemia moderately inhibitory effect could be recognized in the descending order of nitromin, colcemid, urethane, tespamin and myleran; of them nitromin proved to be more effective. 6. Judging from the effects of these agents on leukemic cells in the treatment of leukemias, one might anticipate the efficacy of these drugs as follows: i. e. in acute myelogenous leukemia nitromin is most effective; in chronic myelogenous leukemia nitromin and myleran are most effective; in chronic lymphocytic leukemia tespamin and urethane are most effective; and in monocytic leukemia nitromin is most effective.