The discovery and characterization of growth regulatory genes, in the form of oncogenes, and their counterparts, tumor suppressor (TS) or antioncogenes, has vastly expanded the basic understanding of tumorigenesis. Human solid tumors, such as colorectal cancer, for which the molecular genetics have been most clearly defined, display progressive evolution from cellular dysplasia to anaplasia and metastasis through the stepwise accumulation of genetic defects, involving the regulation and expression of both oncogenes and TS genes. The study of basic genetic abnormalities in melanoma and the identification of the most fundamental of these is critical both to the understanding of abnormal melanocyte proliferation and its potential pharmacologic or immunologic regulation, and also to the identification and screening of patients at high risk for the development of melanoma. The search for such genetic abnormalities has included an analysis of melanomas for defects in known characterized oncogenes and TS genes, and, more importantly, the use of families with hereditary melanoma (HM) and dysplastic nevi in an endeavor to find the melanoma gene. The importance of HM is fundamental, since in the case of other hereditary cancer syndromes for which the genetic basis has been identified, the same or similar genetic abnormalities underlie sporadic tumors of the same tissue type. Thus HM is likely to be the major signpost to the melanomagenic defect.