A review is presented of the literature concerning the placenta as a target organ for chemical- and drug-induced injuries that can ultimately lead to teratogenesis or reproductive defects. Such defects can result from the effects of xenobiotics on placental transport, blood flow or pathology, from the metabolism by the placenta of xenobiotics to harmful substances, or from the alteration by xenobiotics of placental endocrine function. Although it is clear that drug- or chemical-induced placental toxicity should be considered as a possible mechanism of teratogenicity, it is an area of research that has been comparatively neglected and is in need of extensive investigation.