1) Progressive anemia was induced in the rabbits injected with collargol, and reticulocytes and nucleated erythrocytes in blood first increased and then gradually decreased. Myeolgram and tissue picture of their bone marrow presented first excitatory proliferation picture followed by regeneration arrest. 2) As for the values of oxygen consumption and glycolysis of bone marrow of the rabbits made anemic by collargol, in the group given 4 day injections they were enhanced while in the group receiving 4-week injections they were reduced markedly. Values of oxygen consumption and anaerobic glycolysis of each group when compared with respective values of normal rabbits showed statistically significant difference. 3) When collargol solution was added to the bone marrow of normal rabbit directly in vitro, the O(2)-consumption tended to increase slightly in the case when the concentration of the collargol solution was low but it decreased gradually as the concentration grew higher. 4) When the serum of rabbits made anemic by collargol was added directly to the bone marrow of normal rabbit in vitro, oxygen consumption of the bone marrow showed a tendency to increase. 5) In the rabbits irradiated with Co(60), reticulocytes and leucocytes decreased strikingly and in their myelogram a picture of regeneration arrest in the myelocytic cells could be observed. 6) Although no significant difference in O(2)-consumption between the bone marrow of the rabbits irradiated with Co(60) and that of normal rabbits could he observed statistically, the values of glycolysis was reduced markedly and when compared with those of the normal rabbits a significant difference could be seen. 7) When the serum of rabbits irradiated with Co(60) was added directly to the bone marrow of normal rabbit in vitro, the O(2)-consumption of the bone marrow of normal rabbit was increased. 8) From these findings it has been clarified that the sera of the rabbits either made anemic by collargol or irradiated with Co(60) have not an inhibitory action against O(2)-consumption of the bone marrow of normal rabbit such as the sera of hypoplastic anemic patients.