Hydrogen peroxide causes vascular contraction and relaxation and contributes to the pathogenesis of hypertension. We hypothesized that the contractile state of blood vessels governs whether H2O2 causes contraction or relaxation. Hydrogen peroxide (1 micromol/L to 1 mmol/L) concentration-dependently contracted thoracic aorta and vena cava from sham normotensive and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The maximal contraction to H2O2 was 3 times greater in DOCA aorta compared with sham aorta but unchanged in DOCA vena cava compared with sham vena cava. In prostaglandin F2alpha (20 micromol/L)-contracted aorta and vena cava from sham and DOCA rats, H2O2 (1 micromol/L to 1 mmol/L) induced a concentration-dependent relaxation that was impaired in DOCA aorta but not DOCA vena cava. In contrast, in KCl (30 mmol/L)-contracted vessels, maximal H2O2-induced contraction was enhanced 15-fold in sham aorta and 5-fold in DOCA aorta but only 2-fold in sham vena cava. Tetraethylammonium (10 mmol/L), BAY K 8644 (100 nmol/L), and ouabain (1 mmol/L) all enhanced maximal aortic H2O2-induced contraction, whereas only ouabain enhanced venous H2O2-induced contraction. The removal of extracellular Ca2+ reduced H2O2-induced contraction in KCl-contracted aorta, whereas maximal venous H2O2-induced contraction (under basal conditions) was unchanged. Our data suggest that differences in arterial and venous K+ channel activity and extracellular Ca2+ influx are responsible for differences in arterial and venous contraction to H2O2. In DOCA-salt hypertension, arterial but not venous contraction to H2O2 is enhanced, and relaxation to H2O2 is reduced.