CV-3988, rac-3-(N-n-octadecylcarbamoyloxy)-2-methoxypropyl 2-thiazolioethyl phosphate was shown to be a specific inhibitor of platelet activating factor (PAF). This compound in concentrations of 3 x 10(-6) to 3 x 10(-5)M inhibited aggregation of rabbit platelets induced by PAF (3 x 10(-8)M), while it had no effect on the aggregation induced by arachidonic acid, ADP, collagen or A-23187. CV-3988 alone even at a concentration of 10(-3)M had no effect on platelet aggregation. The inhibitory action of CV-3988 on the PAF-induced aggregation was independent of the formation of micelles. The PAF (0.1 to 1.0 micrograms/kg, i.v.)-induced hypotension in anesthetized rats was also inhibited dose-dependently by the i.v. administration of CV-3988 (1 and 10 mg/kg), while the hypotensive actions induced by the i.v. administration of acetylcholine (1 micrograms/kg), arachidonic acid (1 mg/kg), bradykinin (10 micrograms/kg), isoproterenol (1 microgram/kg) and histamine (100 micrograms/kg) were not altered by CV-3988 (10 mg/kg, i.v.). All these findings indicate that CV-3988 specifically inhibits the action of PAF in vitro and in vivo. This is the first report of a PAF antagonist which can specifically inhibit the PAF-induced hypotension as well as the PAF-induced platelet aggregation.