Numerous infants born to women consuming foods contaminated with organic mercury during pregnancy have exhibited severe neurologic sequelae after birth. Because of similarity to the human with respect to reproductive parameters, fetal maturation and placental transport, monkeys (Macaca mulatta and M. arctoides) will be used for the following studies. 1) Localization of methylmercury and sites of damage in the macaque brain are being compared in the fetal and adult monkey. 2) The teratogenic potential of methylmercury in the embryonic macaque will be evaluated. 3) Potential therapeutic measures will be examined where a differentiating organism is involved. 4) Women of child-bearing age also exposed to phenylmercury and mercury vapor. Thus, measurements of placental transfer and fetal toxicity following maternal administration of these substances are to be carried out.