The results of the study of the eff ect of MP-5 and MP-6 myelopeptides on the antibody response, production of reactive oxygen species, IL-1β and IL-10 by peritoneal macrophages of mice against a back- ground of 6 hours of immobilization stress in vivo are presented. The stimulating eff ect of MP-5 and MP-6 on the production of reactive oxygen species and IL-1b by peritoneal macrophages was stimulated 6 hours after their administration. Myelopeptides also neutralized the inhibitory eff ect of immobilization stress on zymosan-induced production of reactive oxygen species by peritoneal macrophages and the antibody formation in the spleen.