Chromosome studies of human melanocytic tumors have demonstrated non-random karyotypic abnormalities of chromosomes 1, 6, 7, 9, and 10. These visible genetic alterations may provide clues to the location of oncogenes and suppressor genes involved in the development of lesions from benign nevus to metastatic melanoma, and to the mechanisms by which the function of these genes is altered. To date, however, none of the specific growth regulatory genes important in this neoplastic progression has been identified, with the possible exception of the erbB oncogene in the later stages. Recent results in other human tumors do suggest, however, that the combined cytogenetic and molecular genetic approach will soon lead to the recognition of a number of important genes, both inherited and somatically altered, and that significant clinical applications will follow.