There is a sense of excitement in contemporary cancer research, generated largely by the discovery, and subsequent characterization, of oncogenes. These genes are part of the normal complement of cells, and become altered in their structure or expression, during the development of the neoplastic phenotype. In this review, I highlight some of the important advances in the field, starting with the relationships between viral oncogenes and their cellular homologs. I illustrate some of the molecular mechanisms whereby a harmless, or quiescent, cellular gene can be converted ("activated") by radiation or by other carcinogens to a full-blown oncogene involved in carcinogenesis. Next, I discuss two areas where oncogene research has specific relevance for professionals working with radiation, namely the question of radiation-induced cancer, and the issue of the radiocurability of tumors. I also assess the important role of tumor-suppressor genes in oncogenesis. I then describe a genetic model, to illustrate the current status of our understanding of carcinogenesis. Finally, I discuss potential applications of specific interest to oncologists: topics such as prognostic indicators, novel therapeutic strategies, and gene-replacement techniques, are critically reviewed.