Various experimental anemias have been induced in adult rabbits mainly centering around the hematopoietic functions of the bone marrow; and with continuous observations on the changes of sideroblasts, a series of comparative studies between the sideroblasts and serum iron has been carried out; and obtained the follwing results: 1) The proportion of sideroblasts in normal rabbits is lower and the extent of the sideroblast appearance less extensive than that in the normal persons. 2) The proportion of sideroblasts increases in such anemias where there is a decline in the erythropoietic function as in benzol, collargol, x-irradiation anemia, whereas it returns to normal level at the time when the benzol anemia is recovering. 3) The proportion of sideroblasts either decreases or becomes nil in acute and chronic hemorrhagic anemias where there exist an increase in the erythropoietic function and iron deficiency. 4) In the case which is in the process of hemolysis such as in the phenylhydrazine anemia, the proportion varies according to the period; and it shows no marked change at the extreme periods while it increases at the time of recovery. Furthermore, no significant change can be observed in the saponin anemia. 5) Parallel relationship between sideroblasts and serum iron is not always clearly noticeable, but the two seem to be always in the state labile to utilization. Again, this stainable iron in erythroblasts is understood to be directed solely for utilization and is by far the most labile to iron utilization. 6) From these observations, it may be said that the changes of sideroblasts or of this stainable iron, are dependent upon the conditions of equilibrium existing between the iron supply by serum iron and the utilization of iron controlled by hematopoietic functions.