Hypoxic-ischemic encephalopathy is still a very important cause of neonatal mortality and morbidity. Recently, platelet-activating factor (PAF) has been accused of being responsible for the neuronal damage in hypoxic-ischemic brain. We investigated tissue PAF concentrations in hypoxic-ischemic brain injury in immature rats. Endogenous PAF concentration in brain tissue showed a marked increase in hypoxic-ischemic pups (85.6 +/- 15.5 pg/mg protein) when compared to that of control (9.05 +/- 3.1 pg/mg protein). In addition, we examined the effects of flunarizine, a selective calcium channel blocker, and Ginkgo biloba extract (EGb 761) on endogenous PAF concentration in hypoxic-ischemic brain injury. Endogenous PAF concentrations in both flunarizine-pretreated (16.6 +/- 4.8 pg/mg protein) and EGb 761-pretreated (33.5 +/- 8.9 pg/mg protein) pups were significantly lower than the untreated group. These results indicate that PAF is an important mediator in immature rat model of cerebral hypoxic-ischemic injury. The suppressor effect of flunarizine and EGb 761 on PAF production may open new insight into the treatment of hypoxic-ischemic brain injury.