In the tissue culture of the bone marrow from the rabbits previous given a single injection or successive injection of sera from the patients with hypoplastic anemia or Banti's the author obtained the following results. 1. In the case of a single injection, be it the serum of hypoplastic anemia or Banti's disease, no direct influence can be observed in the rabbit bone marrow. 2. In the case of successive injections with the serum of hypoplastic anemia both erythropoiesis and leucopoiesis are markedly decreased. 3. Even in the case of successive iujections with the serum of Banti's disease likewise both erythropoiesis and leucopoiesis are markedly decreased. 4. In the case injected with the serum obtained from ihe splenectomized patient with Banti's disease no influence on hematopoiesis of the bone marrow can be recogized. 5. After seven successive injections with either one of the sera, if the animals are left without any further treatment, the bone marrow functions at the recovery stage of anemia are back at the normal level. 6. Comparing the in vivo influences of both sera on the bone marrow, when injected successively, the injection of the serum from hypoplastic anemia mainly disturbs the production of bone marrow cells, while the injection of Banti's disease serum inhibits the production of bone marrow cells in some case while it hihibits the maturation of bone marrow cells in other. And the disturbance of the former on the bone-marrow parenchyma is stronger than that in the latter.