Since Ras proteins negotiate many signalling pathways leading to cell growth or differentiation, the regulation of Ras activity is vital to cellular health. Ras activity, which derives from a collaboration between Ras and GTP, is terminated by the GTPase activating protein (GAP)-catalyzed hydrolysis of the GTP. Hence, a simple regulatory scheme emerges: extracellular signals control Ras activity via membrane receptors and GAPs. However, the signalling scenario is probably not so simple. In looking for factors which interpret Ras activity, researchers have been led to the same factors which also regulate Ras activity, namely the GAPs. Therefore, it may be that Ras proteins are actually regulators of GAPs.