The objective was to determine the receptor subtype of angiotensin II (ANG II) that is responsible for vasoconstriction in the nonpregnant ovine uterine and systemic vasculatures. Seven nonpregnant estrogenized ewes with indwelling uterine artery catheters and flow probes received bolus injections (0.1, 0.3 and 1 µg) of ANG II locally into the uterine artery followed by a systemic infusion of ANG II at 100 ng · kg¹ · min¹ for 10 min to determine uterine vasoconstrictor responses. Uterine ANG II dose-response curves were repeated following administration of the ANG II type 2 receptor (AT₂) antagonist PD-123319 and then repeated again in the presence of an ANG II type 1 receptor (AT₁) antagonist L-158809. In a second experiment, designed to investigate the mechanism of ANG II potentiation that occurred in the presence of AT₂ blockade, nonestrogenized sheep received a uterine artery infusion of L-158809 (3 mg/min for 5 min) prior to the infusion of 0.03 µg/min of ANG II for 10 min. ANG II produced dose-dependent decreases in uterine blood flow (P < 0.03), which were potentiated in the presence of the AT₂ antagonist (P < 0.02). Addition of the AT₁ antagonist abolished the uterine vascular responses and blocked ANG II-induced increases in systemic arterial pressure (P < 0.01). Significant uterine vasodilation (P < 0.01) was noted with AT₁ blockade in the second experiment, which was reversed by administration of the AT₂ antagonist or by the nitric oxide synthetase inhibitor N-nitro-L-arginine methyl ester. We conclude that the AT₁- receptors mediate the systemic and uterine vasoconstrictor responses to ANG II in the nonpregnant ewe. AT₂-receptor blockade resulted in a potentiation of the uterine vasoconstrictor response to ANG II, suggesting that the AT₂-receptor subtype may modulate uterine vascular responses to ANG II potentially by release of nitric oxide.