Honokiol, a constituent extracted from Magnolia officinalis, had been shown be an antioxidant and an anti-platelet agent in biological systems with an anti-arrhythmic effect and a myocardial protective effect on ischemia-reperfusion injury. We examined the neuroprotective effect of honokiol in rats subjected to focal cerebral ischemia. Honokiol was administered intravenously either at fifteen minutes before right middle cerebral artery occlusion (pretreatment groups) or when both common carotid arteries clips were removed (treatment groups). The results showed that there was no significant hemodynamic change after intravenous infusion of honokiol at the dosages of 10(-8), 10(-7) and 10(-6) g/kg in both groups. However, honokiol significantly reduced the total volume of infarction at the doses of 10(-7) or 10(-6) g/kg in both pretreatment and treatment groups. This study suggests that honokiol is a potent neuroprotective agent in focal cerebral ischemia. This beneficial effect may be related to its antioxidant effect and anti-platelet aggregation activity.