The ability of foreign compounds to affect the functioning of various endocrine systems is currently thought responsible for a wide variety of effects. The presentations in this Symposium reviewed the evidence for and against the involvement of endocrine systems in several different aspects of reproduction. The mechanism behind the ability of a triazine herbicide to cause enhanced appearance of mammary tumors in one strain of female rats is reviewed by Stevens. The data suggest that enhanced aging, not direct mammary modulation, is responsible. Dietary phytoestrogens, the mediators of their actions, their effects in various biological systems, and the relationships between phytoestrogen producers and consumers are all provocatively and succinctly reviewed by Hughes. Kelce presents the strategy used to dissect the mode and mechanisms of action of a fungicide that opened a new awareness in reproductive toxicology: the possibility of xenobiotics being antiandrogens. Finally, to heighten our understanding of the interplay among hormonal systems in vivo, Hess reviews the data that show that androgens are not the only hormones important in the development of the male reproductive system: the pituitary is shown to play a critical role at specific stages of development. The breadth of these presentations, and the implications of their findings, should make us pause and realize how much there is still to discover about the interaction between the reproductive system and anthropogenic compounds.