All components of the renin-angiotensin system (RAS) are present in the kidneys and constitute a functioning renal RAS. Angiotensin II (Ang II) receptor subtypes AT₁ and AT₂ have been identified in the afferent and efferent arterioles, glomeruli, mesangial cells, and proximal tubules. AT₁ receptors regulate vasoconstriction and sodium and water reabsorption, as well as promote cell growth, proliferation, and collagen matrix deposition. Recent animal studies are elucidating the role of the less well understood AT₂ receptors. The AT₂ receptors appear to counterbalance the AT₁ receptors by increasing the production of bradykinin, nitric oxide, and cyclic guanosine monophosphate—mediating vasodilation and by promoting cell differentiation, antiproliferation, and apoptosis. Ang II subtype 1 receptor blockers prevent Ang II activation of the AT₁ receptor while leaving the AT₂ receptor open to Ang II stimulation.