Experiments on CBA/Ca Lac mice showed that pantohematogen, a drug prepared from whole blood of Siberian deer, wapiti, and deer, when administered in a course in doses under study and in chosen conditions of the experiment does not possess allergenic and immunotoxic properties. The immunomodulating properties of the drug were characterized by marked stimulation of macrophage phagocytic activity and, under definite conditions, by activation of formation of antibody-producing cells in the spleen of mice immunized with sheep erythrocytes.