Because during development, critical molecular and cellular processes must respond with integrity to a variety of hormones and other growth factors to insure normal postnatal function, there is real potential for environmental chemicals to affect these processes. The development of normal reproductive capacity may offer particularly susceptible targets for toxins. Environmental factors might alter the genetic determinants of gonadal sex, the hormonal determinants of phenotypic sex, fetal gametogenesis, reproductive tract differentiation, as well as postnatal integration of endocrine functions and other processes essential for the propagation of the species. While the effects of environmental agents on sexual differentiation and the development of reproductive capacity are largely unstudied, a number of chemicals with diverse structures and actions have been shown to exert dramatic effects, especially on hormone synthesis and function. An attempt has been made here to summarize development processes, to suggest the toxic action of chemicals and describe their effects, and to outline areas for further study.