In order to clarify the effects of surgical intervention on the function of the RES, we performed pseudo-surgical intervention on dogs by the Glycyrrhizin (59)Fe-colloid, and obtained the following results. 1. In the study of the phagocytic function of the RES it was found that simple laparotomy rather accelerates the RES function slightly while in the case of a greater surgical intervention, such as an extensive removal of lymph nodes in the upper abdominal cavity, a marked primary acceleration of the RES function can be observed. In the case of splenectomy performed for the purpose to decrease the quantity of RES tissue, the function is lowered in proportion to the quantity of the tissue removed. 2. As for the hemoglobin synthesis resulting from the iron metabolism of reticuloendothelial cells, a marked acceleration of the function is observed in the case of simple laparotomy, while on the contrary, a strong inhibition is induced by the extensive lymph-node removal of the upper abdominal cavity. In the case of splenectomy such an inhibitory effect on the RES becomes more pronounced when a greater quantity of lymph-node tissue is removed. 3. In the observations conducted on the accumulated total iron and iron fractions in the liver, spleen and bone marrow at 48 houres after anesthesia, it was demonstrated that as the surgical intervention becomes more extensive, there occurs blockade of hemosiderin, and likewise in splnectomy iron accumulation is brought about by the residual spleen but the ratio of hemosiderin to ferritin is reversed, indicating that a strong compensatory function is rendered to the residual spleen. 4. In the study of various functions such as phagocytosis, disposal and synthesis of the entire RES, when the lymph nodes are removed extensively in the upper abdominal cavity, phagocytosis is accelerated only at early stage, but there appears a division of the function as both organic iron and hemoglobin synthesis counteract one another, and in the case of splenectomy the residual spleen exhibits a marked compensatory function, and the compensatory capacity of the liver is also considerable. However, the RES as a whole has been demonstrated to function lesser in proportion to the quantity of the spleen removed. From these findings it has been elucidated that the removal of the organs from RES affects specifically the functions of each organ, giving valuable criteria for clinical study. Further, it was shown that for the study of RES this Glycyrrhizin (59)Fe-colloid method is superior to the available classical metdod.