Mammary gland is assumed to function as a part of the common mucosal immune system. Lymphocytes observed in the mammary gland derived their origin from precursor immunocompetent cells presented in BALT and GALT. In relation to local immunity of the other sites of the mucosal membranes, lymphocytes homing to the mammary gland are regulated by lactogenic hormones. The other peculiarity of the mammary gland mucosal immunity is a direction of the milk protective factors. The secretory products of lactating mammary gland provide a protection not for own organism, but for newborn infant. The human neonates are essentially devoid of differentiated mechanisms of the secretory immunity. The low IgA level and high free Sc level in newborn secretions reflect the immaturity of the mucosal immunity in the neonatal period. But some evidences suggest the activation and fast maturation of newborn mucosal immunity. There were shown the sharp rises of IgA levels in different newborn's secretions during the neonatal period. Using as an object for the study on the neonatal mucosal immunity the newborn mammary gland, we detected the higher level of Ia-positive cells in neonatal milk in relation to maternal milk, in spite of the low level of Ia-positive cells in newborn's blood. Local immunity seems to function, at least partially, independently on systemic functions in neonates. Significant influence on the development of newborn mucosal immunity exerts maternal milk. The circumstantial evidences support the promoting effect of the human milk on the SIgA synthesis by newborn mucosal membranes. It is impossible to exclude the feasibility of antiidiotypic antibodies presented in human milk actively immunize offspring. At the same time, numerous immunosuppressive factors were found in colostrum. It seems that these factors can protect the newborn immune system against overstimulation by large number of environmental antigens. Human colostrum and milk provide also to neonate numerous soluble and cellular factors of passive immunization. Thus, we can say that human milk serve as a connection link between maternal and newborn immune system, and the main role in mother/newborn interrelations plays the local immunity.