Myelopeptides MP-3, MP-5, and MP-6 were found to suppress zymosan-induced production of reactive oxygen species by leukocytes both under one-way introduction and under pretreatment. All of myelopeptides under examination in case of one-way introduction in cultures with zymosan demonstrated a decrease in zymosan-stimulated (1500 mkg/ml) production of IL-1beta, and activation of spontaneous production of this cytokine by whole blood cells. TNF-alpha production under myelopeptide effect was lowered in cultures with 150 mkg/ml zymosan. Under pretreatment myelopeptides did not render effect on IL-1beta and TNF-alpha production, with the exception of single stimulating effect of MP-5 on IL-1beta level in spontaneous cultures. Using comparative analysis the difference in direction and expressivity of effects of various myelopeptides was not revealed that suggests the existence of common mechanism of action in this group of peptide bioregulators.