The effects of N omega-nitro-L-arginine (nitroarginine), an inhibitor of endothelium-dependent relaxing factor (EDRF) production, on vascular tone and responses to vasodilator and vasoconstrictor agents were investigated in the hindquarters vascular bed of the cat. Under constant flow conditions, infusion of nitroarginine into the hindquarters vascular bed caused a significant increase in systemic arterial and hindquarters perfusion pressures. During infusion of nitroarginine, hindquarters vasodilator responses to acetylcholine and bradykinin were reduced significantly whereas vasodilator responses to isoproterenol, PGE1, nitroprusside, and 8-bromoguanosine 3',5'-cyclic monophosphate were not altered. Infusion of nitroarginine significantly enhanced vasoconstrictor responses to the thromboxane receptor agonist U 46619 and to phenylephrine. The results of these studies are consistent with the hypotheses that EDRF production may involve the formation of nitric oxide or a nitroso compound from L-arginine, and that EDRF production may play a role in the regulation of vascular tone and in the mediation of responses to the endothelium-dependent vasodilators, acetylcholine and bradykinin, in resistance vessels in the hindquarters. These data support the concept that EDRF is very likely an endogenous nitrovasodilator derived from L-arginine in the hindquarters vascular bed of the cat.