In the series of this experiments, it was revealed that the reticulo-endothelial system plays a great role in the iron metabolism. The loosely bound colloid iron, whose iron is proved to be easily utilized for hemoglobin-synthesis by intravenous adminstation, is deposited in RES. In this report, the observations on the iron metabolism in the animals having RES blocked with Indian ink and gold colloid sol are presented. The anemic rabbits whose RES is blocked showed a normal decrease in serum iron level but a delayed incorporation of iron into both hem and non-hem fractions of erythorcytes, when Fe(59) is given intravenously as S. I. C.; i. e. hemoglobin synthesis is slightly delayed in the case of gold colloid sol block and markedly in Indian ink block, reaching the normal level after one week in both cases. Histologic observation after the iron adminstration proved the blocked RE-cells can phagocytize the iron colloid. Observation on 13th experimental day showed only the blocking substance but not iron. From these observations the effect of block in RES is mainly in the disturbances of the utilization of the ingested iron but not the phagocytic function itself, though these will be closely related to the nature and the quantity of the materials used for blocking.