Cardiac atrial natriuretic peptide (ANP) participates in the maintenance of arterial blood pressure and intravascular volume homeostasis by concerted renal, adrenal, vascular and central nervous actions. These various cellular effects are mediated by the guanylyl cyclase-A (GC-A) receptor and intracellular cGMP. Within the vascular system the GC-A receptor is densely expressed both in smooth muscle and endothelial cells. To dissect the functions of these vascular action sites of ANP in vivo, we inactivated the GC-A gene selectively in one of both cell types, using Cre-lox technology. Remarkably, smooth muscle-restricted deletion of GC-A in mice completely abolished the direct vasodilating effect of ANP but did not affect resting arterial blood pressure and volume. In contrast, mice with endothelial GC-A deletion, despite the preservation of the diuretic and vasodilatating effects of ANP, have marked chronic hypervolemic hypertension. Furthermore, acute vascular volume expansion, which caused release of endogenous cardiac ANP, did not affect resting central venous pressure of control mice but rapidly and significantly increased central venous pressure of mice with endothelial GC-A deletion. Our intravital microscopy studies showed that ANP, via endothelial GC-A and the downstream cGMP-dependent kinase (cGK I), increases the microvascular extravasation of albumin in the skin and skeletal muscle. Investigations in vivo and in cultured microvascular endothelial cells indicated that caveolae-mediated albumin transcytosis is one mechanism mediating this effect. The ANP/GC-A–induced plasma proteins escape across capillary walls increases interstitial oncotic pressure and ultimately can shift fluid from the intravascular to the interstitial compartment to maintain intravascular volume homeostasis.