In the course of history, humans have attempted to interrupt the physiological and psychological bond formed between a nursing mother and her child by substituting breastfeeding with artificial formulas. A growing body of evidence indicates that breast milk, quite apart from its unsurpassed nutritive value, contains a large number of substances that protect the offspring from common infectious agents and allergens and promote the maturation of the gastrointestinal tract and the immune system. In addition to well described milk antibodies and soluble mediators of innate immunity, milk cells and pluripotent secreted factors - cytokines - are currently in the forefront of extensive research with respect to their importance in milk immunology. The purpose of this conference was to critically evaluate the current state of our knowledge concerning the protective role of immune agents found in milk, to provide up-to-date information of milk factors with respect to their role in the maturation of immunological defense systems in the neonate, and to reassess the importance of breastfeeding in the prevention of allergies in formula-fed infants. We hope that the work presented by international participants will prompt many new ideas and stimulate further research in this important area. This conference was sponsored primarily by the National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD. We would like to thank Drs. Sumner Yaffe and Delbert Dayton for their efforts with the organization, planning, and support of this conference.