The author performed the bone-marrow tissue culture of various leukemic patients in fluid medium with addition of several anti-leukemic chemical agents, and observed changes in the leucocyte count from time to time, and conducted the screening of these agents. The results of the experiment are as follows. In acute myelogenus leukemia the inhibitory effect was found to be in the descending order of Prednisolone, Cortisone and ACTH; in chronic myelogenous leukemia it was in the order of 6MP and Prednisolone; in acute lymphocytic leukemia Prednisolone, ACTH and Cortisone; in chronic lymphocytic leukemia Prednisolone, ACTH, and Cortisone; and in monocytic leukemia 6MP and Prednisolone.