Ras proteins are distributed in different types of plasma membrane microdomains and endomembranes. However, how microlocalization affects the signals generated by Ras and its subsequent biological outputs is largely unknown. We have approached this question by selectively targeting RasV12 to different cellular sublocalizations. We show here that compartmentalization dictates Ras utilization of effectors and the intensity of its signals. Activated Ras can evoke enhanced proliferation and transformation from most of its platforms, with the exception of the Golgi complex. Furthermore, signals that promote survival emanate primarily from the endoplasmic reticulum pool. In addition, we have investigated the need for the different pools of endogenous Ras in the conveyance of upstream mitogenic and transforming signals. Using targeted RasN17 inhibitory mutants and in physiological contexts such as H-Ras/N-Ras double knockout fibroblasts, we demonstrate that Ras functions at lipid rafts and at the Golgi complex are fully dispensable for proliferation and transformation.P.C.’s laboratory is supported by grants BMC2002-01021 and GEN2003-20239-C06-03 from the Spanish Ministry of Education and grant 01-087 from the Association for International Cancer Research. E.S.’s laboratory is supported by grants SAF2003-04177 and GEN2003-20239-C06-02 from Spanish Ministry of Education and FIS PI/021570 from Spanish Ministry of Health. D.M. is an I3P program postdoctoral fellow. V.S. is a Lady Tata Memorial Trust postdoctoral fellow. I.A. is a Fundación Valdecilla postdoctoral fellow. L.A.-I. and F.C. are Spanish Ministry of Education predoctoral fellows.Peer reviewed