There is a family of homologous proteins known to small GTP-inding proteins which have a GTP binding domains and GTPase activity with molecular weight of about 20000 in mammalian tissues. Recently at least 20 different small GTP-binding proteins including three rasproto-oncogene, smg25, rho, and ral gene products were identified. These proteins play a central role in cellular prolifration, neoplasia, signal transduction, terminal differentiation, and secretory process of the cells. In this review, I have briefly compiled current information on the different areas of research in the small GTP-binding proteins in an attempt to convey an overall view of the fundamental role that this family of protein in normal cellular processes. Moreover, furture goals of research in the small GTP-binding proteins as well as the possible existence of this family of proteins in plant cells were discussed.