The pioneering work of Furchgott, Moncada, and Vane has clearly established that the endothelium plays a critical role in the regulation of vascular tone. The endothelium produces several potent vasoactive substances, including vasodilators such as endothelium-derived relaxing factor and prostacyclin as well as vasoconstrictors such as angiotensin II and endothelin. These vasoactive substances not only have short-term effects on vascular tone but also appear to induce long-term effects on vascular structure. This process of vascular remodeling involves cell growth or regression and extracellular matrix expansion or contraction. As the interface between the bloodstream and the vessel wall, the endothelium plays a pivotal role in sensing and transducing the stimulus that induces vascular remodeling as well as producing the mediators that alter cell growth and the composition of the extracellular matrix. The endothelium maintains homeostasis within the vasculature by a balance between vasodilators and vasoconstrictors or growth inhibitors and growth promoters. Endothelial cell dysfunction may alter the delicate balance of mediators necessary to maintain homeostasis. Indeed, endothelial cell dysfunction is a common pathogenetic defect in animal models of hypertension as well as in hypertensive humans. Further understanding of the cellular and molecular mechanisms of vascular remodeling induced by endothelial cell-derived mediators may have important implications in the pathogenesis and treatment of hypertension.