Recent findings reporting the structure, the mechanism of action of peptide growth factors and their receptor as well as their presence in human tumors have led to a better knowledge of the events involved in cell growth regulation. The ability of cancer cells to produce and to respond to their own growth factors confers on them a growth autonomy and strengthens the link between growth factors and oncogenes. Oncogenes render the cells growth factor-independent not only by coding for autocrine growth factors of their receptor, but also by amplifying the mitogenic signals generated by the binding of the peptide growth factor to its membrane receptor.