Since the mid-eighties, numerous small G-proteins of the ras gene superfamily have been identified and characterized; more than sixty members are distributed into four subfamilies: ras, rho, rab and ran. Although it appears that, structurally, the products of the ras superfamily are related and implicated in various and diverse intracellular mechanisms: signal transduction, cell cycle, differentiation, cellular traffic, etc., their true and specific functions and their scope and extent are still largely unknown for many of them. Approaches to unravel their function include: determination of their intracellular localization, differential expression in various cell and tissues, phenotypic changes induced by the active forms, studies of the interacting molecules. Recent studies combining advanced mammalian cell biology/biochemistry and genetic studies in yeast might help elucidate the specific role exerted by these proteins.