Hypertension is considered to be the most important risk factor in the development of cardiovascular disease. An increasing body of evidence suggests that oxidative stress, which results in an excessive generation of reactive oxygen species (ROS), has a key role in the pathogenesis of hypertension. The modulation of the vasomotor system involves ROS as mediators of vasoconstriction induced by angiotensin II, endothelin-1 and urotensin-II, among others. The bioavailability of nitric oxide (NO), which is a major vasodilator, is highly dependent on the redox status. Under physiological conditions, low concentrations of intracellular ROS have an important role in the normal redox signaling maintaining vascular function and integrity. However, under pathophysiological conditions, increased levels of ROS contribute to vascular dysfunction and remodeling through oxidative damage. In human hypertension, an increase in the production of superoxide anions and hydrogen peroxide, a decrease in NO synthesis and a reduction in antioxidant bioavailability have been observed. In turn, antioxidants are reducing agents that can neutralize these oxidative and otherwise damaging biomolecules. The use of antioxidant vitamins, such as vitamins C and E, has gained considerable interest as protecting agents against vascular endothelial damage. Available data support the role of these vitamins as effective antioxidants that can counteract ROS effects. This review discusses the mechanisms involved in ROS generation, the role of oxidative stress in the pathogenesis of vascular damage in hypertension, and the possible therapeutic strategies that could prevent or treat this disorder. Hypertension Research (2011) 34, 431-440; doi:10.1038/hr.2010.264; published online 13 January 2011Keywords: antioxidants; endothelial dysfunction; oxidative stress INTRODUCTION Hypertension is considered the most important risk factor for the occurrence of cardiovascular disease. 1 Oxidative stress has gained attention as one of the fundamental mechanisms responsible for the development of hypertension. Reactive oxygen species (ROS) have an important role in the homeostasis of the vascular wall; hence, they could be part of the mechanism that leads to hypertension. 2-4 Thus, increased ROS production, reduced nitric oxide (NO) levels and reduced antioxidant bioavailability were demonstrated in experimental and human hypertension. Vascular superoxide is primarily derived from nicotinamide adenine dineucleotide phosphate (NADPH) oxidase when stimulated by hormones, such as angiotensin II (AT-II), endothelin-1 (ET-1) and urotensin II. In addition, increased ROS production may be generated by mechanical stimuli on the vascular wall, which increase with hypertension. ROS-induced vasoconstriction results from increased intracellular calcium concentration, thereby contributing to the pathogenesis of hypertension. 2 Vasomotor tone is dependent on a delicate balance between vasoconstrictor and vasodilator forces that result from the interaction between the components of...