AbstractOral administration of high dosages of the dithiocarbamate pesticides maneb and mancozeb was teratogenic in rats but not in mice. The malformations, severe limb and craniofacial defects, were pronounced after maneb treatment but less so after mancozeb and propineb, zinc‐containing compounds. The teratogenic effect of maneb was progressively reduced by simultaneously adminstering increasing amounts of zinc acetate. The mechanism of the teratogenic effect may involve the compounds being chelating agents, trapping zinc required for many important enzyme systems.