The ultimate goal of all genetic analyses, whether at the statistical or molecular level, is to identify individual genes and their function. The application of genetic epidemiological tools to common diseases, together with the recent implementation of recombinant DNA methodology, makes it feasible to identify, characterize, and even isolate genes involved in the major diseases of mankind. This paper outlines how the classical epidemiologic approach interfaces with the new DNA technologies. We review the progress of restriction fragment length polymorphism analyses in family studies and address their current and potential use in studies of unrelated individuals. In addition, we briefly discuss the role that oncogenes and inherited genetic alterations seem to play in the development of human cancers. The use of these techniques provides a framework for a better understanding of cancer etiology and may eventually help to define strategies for cancer prevention.