We have examined the time course of brain edema and the blood-brain barrier opening in rat after basal ganglia ischemia induced by photothrombotic occlusion of the small vessels within the caudate-putamen. Male SD rats were anesthetized, and Rose Bengal dye was intravenously injected. The left caudo-putamen was exposed to cold white light for 5-10 min via a stereotaxically implanted optic fiber. Ischemic brain edema and the blood-brain barrier, as well as the histological changes, were assessed at various times during the following 6 weeks. Local cerebral blood flow was measured 90 min after photothrombosis by quantitative autoradiography. A round infarct with thrombosed parenchymal vessels surrounded by a layer of selective neuronal death was formed within the caudo-putamen. The ischemic lesion turned into a lacune over a period of 6 weeks. A central zone of markedly reduced blood flow and a surrounding oligemic zone were observed 90 min after light exposure. Early blood-brain barrier opening with edema was observed as early as 4 h after photothrombosis, peaked at day 1, and disappeared at 7 days after photothrombosis. In a model of lacunar infarction, we observed an early and transient brain edema and blood-brain opening after onset of ischemia.