In this short overview of oncogenes and cell growth, the protein products have been divided into two classes, proto-oncogenes and oncogenes. Proto-oncogenes can be activated by point mutations and deletions. Two classes exist: the dominant, which leads to cell growth and the suppressor, which by definition suppresses growth. The mechanism of action is multiplex--duplication of hormone action, resemblance to receptors, or kinases and DNA binding proteins. It is clear that the regulation of cell growth and differentiation is very complex and that the products of proto-oncogenes play important roles in this regulation. Their functions appear to be at two levels. The first level is that of transduction of signals to the nucleus where the signals can be acted upon. The second is at the level of specific gene regulation, where incoming signals are turned into a response by the cell through activation of specific genetic programs. Nuclear proto-oncogene products play intimate roles in activation of these programs. The nature of the specific target genes regulated in response to these oncogene and proto-oncogene products however, remains a critical area of intensive research.