NADPH oxidases (NOX) are the major source of reactive oxygen species (ROS) in the vasculature and contribute to the control of renal perfusion. The role of NOX2 in the regulation of blood pressure and afferent arteriole responsiveness was investigated in NOX2^-/- and wild-type mice. Arteriole constrictions to AngII (10^-14 - 10^-6 mol/l) were weaker in NOX2^-/- compared to wild-type. L-NAME (10^-4 mol/l) treatment reduced basal diameters significantly more in NOX2^-/- (-18%), than in wild-types (-6%), and augmented AngII responses. Adenosine (10^-11 - 10^-4 mol/l) constricted arterioles of wild-types but not of NOX2^-/-. However, simultaneous inhibition of adenosine type-2 receptors induced vasoconstriction, which was stronger in NOX2^-/-. Adenosine (10^-8 mol/l) enhanced the AngII response in wild-type, but not in NOX2^-/-. This sensitizing effect by adenosine was abolished by apocynin. Chronic AngII pretreatment (14 days) did not change the AngII responses in NOX2^-/-, but strengthened the response in wild-type. AngII pretreatment augmented the L-NAME response in NOX2^-/- (-33%), but not in wild-type. Simultaneous application of L-NAME and AngII caused a stronger constriction in the NOX2^-/- (-64%) than in wild-type (-46%). Basal blood pressures were similar in both genotypes, however, chronic AngII infusion elevated blood pressure to a greater extent in wild-types (15±1%) than in NOX2^-/- (8±1%) mice. In conclusion, NOX2 plays an important role in the control of afferent arteriole tone, and is involved in the contractile responses to AngII and/or adenosine. NOX2 can be activated by elevated AngII and may play an important role in AngII-induced hypertension. NOX2 derived ROS scavenges NO, causing subsequent NO-deficiency.