We tested whether gender influences cerebrovascular responses to angiotensin II (AngII) and the role(s) of Nox2.AngII-stimulated superoxide (O(2)(-)) production by cerebral arteries from male and female wild-type (WT) and Nox2(-/-) mice was measured using lucigenin- or L-012-enhanced chemiluminescence. Hydrogen peroxide (H(2)O(2)) production was measured using Amplex Red fluorescence. Western Blotting was used to measure expression of Nox2, endothelial nitric oxide synthase (eNOS), angiotensin receptors (AT(1) and AT(2)), and superoxide dismutases (SOD1-3). Immunofluorescence was used to localize Nox2 in middle cerebral arteries (MCA). Vascular responses to AngII were assessed in a perfusion myograph. AngII-stimulated O(2)(-) and H(2)O(2) production by cerebral arteries from female WT mice was approximately 75% to 85% lower than in males (P<0.05). O(2)(-) production was approximately 60% lower in Nox2(-/-) versus WT males (P<0.05), whereas Nox2 deletion did not affect O(2)(-) production in females. Expression of Nox2, eNOS, AT receptors, and SOD isoforms was similar between genders. Nox2 immunofluorescence was similarly localized in adventitial and endothelial cells of MCA from both genders. AngII elicited smaller contractions of MCA from females vs males (P<0.05). Contractions were reduced in male, but not female, Nox2(-/-) mice (P<0.05). The SOD mimetic, tempol, potentiated contractions to AngII in male WT mice (P<0.05), whereas the SOD/catalase mimetic, EUK-134, virtually abolished contractions (P<0.05).AngII-stimulated O(2)(-) and H(2)O(2) production are greater in cerebral arteries from male versus female mice, and are associated with greater contractions to AngII mediated by H(2)O(2). These gender differences are dependent on the expression of Nox2.