Nitric oxide is a multifunctional regulator of the vascular system. In healthy blood vessels, nitric oxide is produced from L-arginine by the constitutive nitric oxide synthase in endothelial cells. In addition, vascular injury or inflammation cause the production of nitric oxide in most types of vascular cells, including vascular smooth muscle. This response to injury is due to the induction of a second type of nitric oxide synthase by cytokines such as interleukin-1 beta or tumor necrosis factor-alpha. Factors derived from blood (thrombin, plasmin) and from vascular cells (platelet-derived growth factor, transforming growth factor beta, insulin-like growth factor, epidermal growth factor and basic fibroblast growth factor), regulate the induction of nitric oxide synthesis in vascular smooth muscle cells. The endogenous production of nitric oxide by vascular smooth muscle at sites of injury may contribute to the local control of blood flow, vascular tone and blood fluidity. It may participate also to the remodeling of the injured blood vessel wall.