Studies of pregnancy outcome have focused primarily on maternal variables. This emphasis on the singular role of the mother in fetal health tends to minimize the likelihood of paternal influences. In contrast to the thalidomide tragedy which led to the acknowledgement that a host of potential toxicants could cross the placenta, reports of paternal effects often focus on the specific inducing agent rather than on the phenomenon itself. Yet epidemiologic and animal studies document male-mediated effects of a broad spectrum of agents. These include: therapeutic and recreational drugs; hazardous chemicals in the workplace and environment. Paternal exposures can result in a variety of abnormal outcomes: spontaneous abortions, stillbirths; growth retardation [fetal, neonatal, crossgenerational]; childhood leukemias, brain tumors; alterations in several behaviors and neuroendocrine function. Intent of this symposium is to offer a more balanced view of the significance of both parents in a successful pregnancy outcome and to encourage research in this area.