Genetic damage is associated with various embryo pathologies; and many teratogens and transplacental carcinogens are known to be genotoxic. The present study was aimed at charaterizing SCE induction levels in rodent maternal, embryonic and extra-embryonic cells after maternal exposure to 4NQO. Tissue-specific assessments were made at various gestational ages, and thus stages of placental development. Embryo liver, and yolk sac - the malfunction of which has been implicated in teratogenic mechanisms were assessed with a particular view to whether they would show relatively low levels of SCE induction and thereby lend support to the concept of a protective placental barrier to 4NQO. A previously established rat system allowing for in vivo SCE induction analyses of maternal marrow and embryo liver or yolk sac was used for these studies.