Rhes is a small GTP-binding protein prominently localized in the striatum. Previous findings obtained in cell culture systems demonstrated an involvement of Rhes in cAMP/PKA signalling pathway, at a level proximal to the activation of heterotrimeric G-protein complex. However, its role in the striatum has been, so far, only supposed. Here we studied the involvement of Rhes in dopaminergic signalling, by employing mice with a null mutation in the Rhes gene. We demonstrated that the absence of Rhes modulates cAMP/PKA signalling in both striatopallidal and striatonigral projection neurons by increasing Golf protein levels and, in turn, influencing motor responses challenged by dopaminergic agonist/antagonist. Interestingly, we also show that Rhes is required for a correct dopamine-mediated GTP binding, a function mainly associated to stimulation of dopamine D2 receptors. Altogether, our results indicate that Rhes is an important modulator of dopaminergic transmission in the striatum.