Solcoseryl is a protein-free extract from calf blood with a high RES activity, and has a remarkably stimulating action on the respiration of cells. Clinically, Solcoseryl is applied on ulcerating diseases and so on. The effects of Solcoseryl on reticulo-endotherial function about the phagocytic and hemoglobin-incorporation activities were studied by the determination of glycyl-lycine (59)Fe colloid in the blood of NC-mice. The results were as follow; 1) Solcoseryl had a slightly stimulating action on the phagocytic activity. 2) Solcoseryl had a remarkably stimulating action on the hemoglobin-incorporation activity.