The continuing goal of this project is to develop equivalent human and rat mammary gland in vitro cell systems that will be used for an organ-specific interspecies comparison of the interaction of chemical carcinogens with these cells. In vitro systems developed for these comparisons may also provide human organ-specific cell systems to evaluate the toxicity of environmental chemicals. To achieve these goals we will first complete the development of equivalent methods to grow human and rat mammary cells in well characterized mass and clonal cultures. These culture systems will be used in both direct and cell-mediated mutagenesis assays. These biological assays, together with the biochemical evaluation of carcinogen metabolism and formation and removal of DNA carcinogen adducts by these mammary cells, will be used to compare the interactions of chemical carcinogens with human and rat mammary cells in vitro. Both intra- and interspecies qualiltative and quantitative differences will be documented. This project will provide and evaluate human organ-specific cell culture systems that may be useful in identifying environmental carcinogen. It will also address the question of interspecies extrapolation of carcinogen-cell interactions.