This study will compare the interaction of chemical procarcinogens with human and rodent cells. Human and rat mammary tissue will be processed to give monodispersed cells. These cells will be divided into stromal and parenchymal populations. These cell populations will be cultured and compared for their abilty to activate chemical procarcinogens to mutagenic compounds. Mutagenesis will be tested in co-cultivated mammalian cell lines. Human and Chinese hamster V-79 fibroblast-like cell lines will be compared for their ability to detect mutagens in this mammary mediated system. In addition to quantitating mutagenesis, we will also examine the carcinogen-DNA reactions in both the activating mammary cells and mutagenesis test-cells by analyzing their carcinogen - deoxyribonucleoside (C-D) profiles. Finally, the C-D profiles of rat mammary cells exposed in vivo and in vitro will be compared. These studies will provide information that may help bridge the animal-human gap in the area of carcinogen action.