BN 52021, a new specific PAF-acether receptor antagonist, was evaluated on several cardiovascular models. BN 52021 antagonized PAF-acether-induced extravasation in rats. Inhibition of the hypotensive action of PAF-acether was obtained by administration of the antagonist, given preventively or curatively. In isolated guinea-pig hearts, BN 52021 inhibited the vasoconstriction induced by PAF-acether whereas a small inhibition was observed with papaverine. On the other hand, phosphodiesterase inhibitors were very effective against coronary vasoconstriction induced by vasopressin while BN 52021 was without effect. PAF-acether increased the tonus of rat isolated portal vein; this effect was inhibited by BN 52021, without any reduction in basal myogenic activity. In this model Ca2+ antagonists (D 600, diltiazem) showed a small inhibitory effect but they strongly reduced basal myogenic activity. Neither PAF-acether nor BN 52021 modified phenylephrine-induced contraction of the isolated rabbit aorta with or without endothelium demonstrating that endothelium-dependent relaxing factor is not related to PAF-acether. Our results suggest that BN 52021 specifically block the cardiovascular effects of PAF-acether. This agent may thus be an useful tool for a better understanding of the role of PAF-acether in hemodynamic changes involved in anaphylaxis or shock.