Sister chromatid exchanges have been used as a sensitive indicator of mutagenesis. In this project, in vivo BrdU methodology is used to detect SCE induction in rat embryos when the pregnant mothers are exposed to known carcinogens 4NQO and Procarbazine. The purpose of these experiments is to explore the use of SCEs in assessing transplacental genetic damage caused by environmental mutagens/carcinogens/teratogens.