In order to compare the influences of various anti-leukemic agents on the bone marrow thrombopoiesis, the clinical tissue culture of bone marrow from normal guinea pigs and healthy persons was conducted. Various anti-leukemic agents were added to the culture media at the maximum concentration where they would not inhibit the bone marrow growth in culture, and observations were carried out to see the influences of these agents on the function of megakaryocytes of bone marrow. As the results, the author arrived at the follwing conclusions. 1. Urethane. Nitromin. Demecolcin, Actinomycin C and Mitomycin C inhibit the thrombopoietic function of bone marrow to a high degree. 2. Thio-TEPA, 8-Azaguanine, Carzinophilin, and Chromomycin demonstrate a moderate inhibitory action on the thrombopoietic function of bone marrow. 3. 6-MP slightly inhibits the thrombopoietic function of bone marrow. 4. Myleran, and the combined use of 6-MP and Prednisolone show no inhibitory effect on the thrombopoietic function of bone marrow. 5. On the other hand, Prednisolone alone rather augments the bone marrow thrombopoietic function.