It has been shown in experiments on 240 mice (lines CBA, C57Bl, their first generation F1 hybrids and animals of mixed breed) that spleen cells of mice immunized by subcutaneous administration of 0.2 ml of pigeon blood are capable of producing the formation of plaques of hemolysis with autologous erythrocytes and rosettes with pigeon erythrocytes. This indicates the immediate participation of cells producing autohemolysins in the specific immune response.