The expression of activated cellular oncogenes in chemically induced rat tumors and the relationship of oncogene expression to progression from the normal to the neoplastic phenotype are studied using 3T3 transfection and hybridization techniques and monoclonal antibodies directed against the specific oncogene products. Four types of tumors have been generated by single injection of F344 rats using direct-acting alkylating agents; renal mesenchymal tumors induced by methyl(methoxy-methyl)nitrosamine (DMN-OMe), intestinal adenocarcinomas induced by methyl(acetoxy-methyl)nitrosamine (DMN-OAc), hepatocellular carcinomas induced by intraportal injection of DMN-OAc followed by phenobarbital promotion, and gliomas induced by transplacental exposure to nitrosoethylurea (ENU). DNA purified from these tumors is utilized for 3T3 transfection assays, which are particularly effective for the detection of the ras oncogene, and in Southern blot hybridizations with available oncogene probes. Activated Ki-ras oncogenes have been identified by 3T3 cell transfection and hybridization techniques in 13 primary renal mesenchymal tumors and in one nasal cavity carcinoma induced by DMN-OMe. Tumor DNA positive for activated oncogenes will be evaluated to determine whether the oncogene is of the wild-type or a mutant by restriction mapping and sequencing. Depending upon availability of oncogene products, hybridoma technology will be applied for the production of monoclonal antibodies specific for the product, and generated monoclonals will be used to characterize oncogene expression in preneoplastic, early and late stages of tumor development in vivo by immunohistochemical procedures.