Peroxyl free radicals and hydroperoxides are readily formed from easily oxidized organic molecules. Recent experiments suggest the peroxyl radicals and hydroperoxides are involved in the initiation and promotion phases of carcinogenesis. Quantitative in vivo data with which to evaluate such hypotheses have been difficult to obtain because of the instability and reactivity of peroxyl radicals and hydroperoxides. This application outlines experiments designed to provide fundamental information about the occurrence and activities of peroxyl radicals and hydroperoxides in two different animal model systems. Research from our laboratory has established that (+)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene is a specific and highly reactive trap for peroxyl radicals. We propose to apply it to mouse skin and quantitate its oxidation products after treatment of the skin with tumor promoters and other agents. This should provide the first direct measurements of the levels of peroxyl free radicals generated in target tissues as a result of pharmacological challenge. We have shown that fatty acid hydroperoxides and fatty acid alcohols stimulate DNA synthesis and induce ornithine dicarboxylase activity in rat colon following intrarectal instillation. This suggests that primary oxidation products of unsaturated fatty acids contribute to the post-initiation phase of colon carcinogenesis. We propose several experiments to test this hypothesis. Analogues will be synthesized to determine precisely the structural requirements for enhancement of epithelial proliferation. Methods will be developed to quantitate the levels of oxidized fatty acid derivatives present in the colonic lumen. Carcinogenesis experiments will be performed to determine the tumor-promoting activity of oxidized fatty acid derivatives in the colon. These studies should provide critical information about a novel class of potential tumor promoters derived from unsaturated fatty acids via peroxyl radicals.