The proposed research is concerned with the interaction of chemical carcinogens with DNA and the consequence (damage and repair) of DNA in vivo will be monitored by an alkaline sucrose gradient method that uses a fluorometric determination of DNA in the gradient fractions. DNA damage and repair will be studied in euchromatin versus heterochromatin. The specificity of different carcinogens to induce damage and then the repair of damage will be compared in the chromatin fractions. The loss of specific alkylated products will be compared between euchromatin and heterochromatin. BIBLIOGRAPHIC REFERENCES: Cox, R. and Irving, C.C. Inhibition of DNA methylation by S-adenosylethionine with the production of methyl-deficient DNA in regenerating rat liver. Cancer Res. 37:222 (1977). Cox, R., Prescott, C., and Irving, C.C. The effect of S-adenosylhonmocysteine on DNA methylation is isolated rat liver nuclei. Biochem. Biophys. Acta 474: 493 (1977).