pp60c-src and the structurally related members of the Src family are non-receptor tyrosine kinases that reside within the cell associated with cell membranes and appear to transduce signals from transmembrane receptors to the cell interior. Many intracellular pathways can be stimulated upon Src activation, and a variety of cellular consequences can result, including morphological changes and cell proliferation. pp60c-src activity is normally suppressed by phosphorylation on its carboxy-terminal tail by an enzyme known as CSK. Various cellular stimuli or mutations within pp60c-src can activate its endogenous kinase activity. In this paper, we review aspects of pp60c-src activation and regulation and discuss results obtained in our laboratory in two experimental systems: (i) in melanoma cell lines and primary pigmented normal human melanocytes and (ii) using activated mutant forms of purified human pp60c-src protein.