Src is a member of the Src family of protein tyrosine kinases. This kinase is expressed in different tissues of the body with the highest protein levels detected in neurons and platelets. Src can modulate the signal transduction pathways activated by several growth factors (e.g., PDGF, M-CSF and G-CSF) and integrins. Src also regulates the activity of several ion channels including the N-methyl-D-aspartate (NMDA) receptor. In addition, Src is thought to play a role in physiological/pathophysiological processes in the central nervous system. It has also been reported that mice deficient in Src develop severe osteoporosis. A total of eight membrane-associated protein tyrosine kinases have been identified within the Src gene family. Members of this group include c-Src, c-Yes, Fyn, Lck, Lyn, Blk and c-Fgr whose roles include regulation of cytoskeletal organization, cell-cell contact, DNA synthesis, proliferation and differentiation of eukaryotic cells. Elevated activity of the proto-oncogene Src has been found in many human cancers, most notably breast cancer.The highest levels of expression of the prototype member of this gene family, Src p60, are observed in platelets and in neuronal tissues. With the fact that platelets have constitutively high levels of phosphotyrosine-containing proteins suggest that Src p60 may be important for platelet homeostasis.