Regulator of G protein signaling (RGS) proteins are regulatory and structural components of G protein-coupled receptor complexes. RGS proteins are GTPase-activating proteins for Gi and Gq class G-alpha proteins. They accelerate transit through the cycle of GTP binding and hydrolysis and thereby accelerate signaling kinetics and termination. RGS5 seems to be an important signalling regulator in the vascular system. Present data suggest that RGS5 may be involved in the regulation of capillary growth, angiogenesis, and in the pathophysiology of stroke.