The central problem in cancer therapy is the poor selectivity of current systemic agents against the common solid tumours. The demonstration that unique segments of DNA, constant in location and conserved in evolution are involved in growth control opens new avenues for basic and clinical research. The function of the products of these genes needs to be elucidated. Examples of growth control functions include homology to growth factors, surface receptors, protein kinases and cell cycle control proteins. From DNA sequence data peptides predicted to be exposed within intact molecules can be constructed and used to produce monoclonal antibodies to oncogene products. Such antibodies have now been successfully used to demonstrate the intracellular localization of gene products as well as the cell cycle regulatory role of the c-myc protein. By having a battery of antibodies against the different gene products their direct clinical application for diagnosis and prognosis has become a reality. Immunohistology and flow cytometry permit the geographical and quantitative analysis of function in normal and neoplastic tissues. Furthermore, by purification and biochemical analysis the molecular basis for their action can be elucidated. It is likely that by the end of the decade new drugs that inhibit oncoprotein function will be available for clinical trial.