Pathological conditions that predispose to cardiovascular events, such as hypertension, hypercholesterolemia, and diabetes, are associated with oxidative stress. These observations and further data derived from a plethora of investigations provided accumulating evidence that oxidative stress is decisively involved in the pathogenesis of endothelial dysfunction and atherosclerosis. Several enzymes expressed in vascular tissue contribute to production and efficient degradation of reactive oxygen species, and enhanced activity of oxidant enzymes and/or reduced activity of antioxidant enzymes may cause oxidative stress. Various agonists, pathological conditions, and therapeutic interventions lead to modulated expression and function of oxidant and antioxidant enzymes, including NAD(P)H oxidase, endothelial nitric oxide synthase, xanthine oxidase, myeloperoxidase, superoxide dismutases, catalase, thioredoxin reductase, and glutathione peroxidase. Data from numerous studies underline the importance of dysregulated oxidant and antioxidant enzymes for the development and progression of atherosclerotic disease in animal models and humans. Specific pharmacological modulation of key enzymes involved in the propagation of oxidative stress rather than using direct antioxidants may be an approach to reduce oxygen radical load in the vasculature and subsequent disease progression in humans. This review focuses on the modulation of expression and activity of major antioxidant and oxidant enzymes expressed in vascular cells.