We previously reported enhanced expression of the p67phoxand gp91phoxcomponents of NAD(P)H oxidase in angiotensin (Ang) II–induced hypertension, suggesting de novo assembly in response to Ang II. To examine the direct involvement of NAD(P)H oxidases in Ang II–induced O2−production, we designed a chimeric peptide that inhibits p47phoxassociation with gp91phoxin NAD(P)H oxidase (gp91ds-tat). This was achieved by linking a 9-amino acid peptide (aa) derived from HIV-coat protein (tat) to a 9-aa sequence of gp91phox(known to interact with p47phox). As a control, we constructed a chimera containingtatand a scrambled gp91 sequence (scramb-tat). We found that gp91ds-tatdecreased O2−levels in aortic rings treated with Ang II (10 pmol/L) but had no effect on either the O2−-generating enzyme xanthine oxidase or potassium superoxide–generated O2−. We infused vehicle, Ang II (0.75 mg · kg−1· d−1), Ang II+gp91ds-tat(10 mg · kg−1· d−1), or Ang II+scramb-tatintraperitoneally in C57Bl/6 mice and measured systolic blood pressure (SBP) on days 0, 3, 5, and 7 of infusion. SBP increased by day 3 in mice given Ang II and Ang II+scramb-tatbut was significantly lower with Ang II+gp91-tat. On day 7, SBP was still significantly inhibited in mice given Ang II+gp91ds-tat, whereas Ang II–induced O2−production was inhibited throughout the aorta as detected by dihydroethidium staining, consistent with the ability of this inhibitor to block the various vascular NAD(P)H oxidase isoforms. These data support the hypothesis that inhibition of the interaction of p47phoxand gp91phox(or its homologues) can block O2−production and attenuate blood pressure elevation in mice.