It has been realized for some time that exposure of the developing neonate from conception through birth to (toxic) environmental agents can affect the subsequent health and well-being of the offspring. While organogenesis (the first eight weeks of human gestation) is recognized to be a highly susceptible period for the induction of malformations, the fetal/neonatal developmental phases are now acknowledged to be just as sensitive for many well-documented developmental deficits, amongst which are immune-related disorders. In addition, developing predominantly from studies of maternal stress during pregnancy, a growing body of literature now exists to show that changes in the neurohormonal milieu of both mother/infant during pregnancy and weaning can change immune potential of the offspring. Perhaps even more provocative, there is data to suggest that immune changes in the pregnant mother can in turn modify behavior in offspring. The review below provides a framework for consideration of many of the factors contributing to such processes, and their possible mechanism(s) of action.