Abstract: In this paper,we determined platelet-activating factor(PAF)of brain and blood in ratat ischemic and reperfusion periods,respectively. The results suggest:PAF of brain and blood in rat at ischemic and reperfusion periods is higher than that of controIs. PAF of reperfusinn period is the highest. Itindicates that PAF plays an important role in all the factors inducing ischemic cerebral vescular disease. Theeffect of PAF on cerebral ischemia is discussed here.