By adding iron or cobalt to the tissne culture in fluid medium of bone marrow from normal and various experimental anemic rabbits the author has observed the alteration in the number of sideroblasts and studied the iron metabolism of erythroblasts. The following are the results. 1. In the case of the bone-marrow tissue culture of normal rabbit supplemented with iron sideroblasts are slightly increased in number. 2. In the case of bensol or collargol anemia hardly any increase can be recognized in sideroblasts by the iron addition. 3. In the case of the rabbit irradiated with 300r. the addition of iron increases sideroblasts in number considerably. 4. In the case of hemorrhagic anemia the addition of iron markedly increases the number of sideroblasts as the iron deficiency state advances in its degree. 5. Hardly any increase in the sideroblast number can be observed in the case of phenylhydrazine anemia supplemented with iron. 6. From these alterations in siderodlasts by the effect of iron addition, it is assumed that non-hemoglobin iron in erythroblasts has an important bearing on the iron uptake of erythroblasts. 7. Cobalt has an action as to direct the iron in erythroblasts towards the heme synthesis because in the case supplemented with iron plus cobalt the increase in the number of sideroblasts is smaller than that supplemented with iron alone.