Using radioactive iron (Fe(59)) the author studied the processes of the iron metabolism at the time when the RES functions are changed and obtained the following results. 1. With the intravenous injection of Fe(59) the author pursued the iron distribution in the viscera of the rabbits with hypoferremia induced by the administration of various adrenocortical hormones and autonomic nerve stimulants, and studied the destiny of disappearing serum iron and investigated what relation these results will have with the RES functions. As the results it has been found that ACTH, DOCA, and acetylcholine seem to act as to accelerate the functions of RES, especially the iron metabolism, and make RES take up the serum iron in the viscera, especially hemosiderin and ferritin fractions of non-hemin iron. In the case of cortisone and adrenalin about the same tendency can be observed but the results are not so distinct as in the former. 2. In the investigation of the iron distribution in the viscera by injecting Fe(59) intravenously to the rabbits whose RES is blocked by collargol, it has been found that on the whole the uptake of iron from serum by RES is decreased when the functions of RES are disturbed.