With the purpose to elucidate the influences of the change in the RES functions on the iron metabolism the author studied the iron metabolism in the rabbits injected with ACTH, DOCA, cortisone, adrenalin, acetylcholine, atropine, and ergotamine, as well as in the rabbits blocked of RES by carbon black solution or by collargol, and obtained the following results. 1. The serum iron is decreased by the administration of such drugs as ACTH, DOCA, cortisone, adrenalin, acetylcholine, atropine and ergotamine. When RES is blocked, the decreasing action on the serum iron by these drugs in suppressed. Therefore, it seems that these drugs act as to accelerate the functions of RES, especially the iron metabolism, and that they make RES take up the serum iron. 2. From the standpoint of the iron metabolism, it has been difficult to find any correlation between the action of these drugs on the RES functions and the influences of these drugs on the RES functions as represented by the phagocytotic ability of foreign substances, the method commonly used in the determination of the RES functions. 3. The results of examination of the iron metabolism at the time when RES is blocked by carbon black or collargol are as follows: (a) the serum iron content decreases at an early stage of the blocking, but it tends to increase at an later stage; (b) at the time when RES is blocked, the rate of iron consumption in the blood in which iron is injected intravenously, is low; and (c) the amount of iron stored in the viscera, especially in the liver, rather tends to decrease. Judging these results with a special reference to RES, the influences of the decrease in the RES functions on the iron metabolism when RES is blocked may be interpreted as to cause a fall in the iron uptake from the blood by RES and to bring about the concurrent decline in the retentive power of iron in RES.