Using a perfusion technique of isolated vessels, constrictor responses to vasopressin (VP) and norepinephrine (NE) were investigated in perfused dog femoral arteries. Both OPC-21268, a selec tive V1-antagonist, and OPC-31260, a selective V2-antagonist, significantly shifted the VP-induced dose response curves to the right without influencing the NE-induced ones. The blocking effects of OPC 31260 were much greater than those of OPC-21268, suggesting that there may probably be functional V1 and V2-receptors in isolated dog femoral arteries that mediate vasoconstriction.