By performing the bone-marrow tissue culture of experimental thrombocytopenic purpura induced by the injection of anti-platelet serum and by studying various aspects of culture findings, the author obtained the following results. 1. When the anti-platelet serum of guinea pig is injected into normal guinea pig, the thrombocytes decrease markedly in number. 2. In repeated injections of anti-platelet serum, with each additional injection the decrease of thrombocytes and bleeding tendency due to the serum injection are inhibited. 3. By the injection of anti-platelet serum there occur a decrease in number of thrombocytes and a bleeding tendency, and such bleeding is marked at the site of injection and also it induces bleedig in the somatic organ tissues, showing a marked bleeding in the lung, heart, stomach and intestines. 4. In the bone-marrow picture of the guinea pig injected with anti-platelet serum, no marked changes can be observable in the erythrocyte and leucocyte series. 5. In the case of the bone-marrow tissue culture of the guinea pig injected with anti-platelet serum, no changes can be recognized in the erythrocyte and the leucocyte series.