The purpose of this study was to investigate the effects of memantine on brain ischemia. Because we can measure nitric oxide (NO) production and hydroxyl radical metabolism continuously, we investigated the effect of memantine on NO production and hydroxyl radical metabolism in cerebral ischemia and reperfusion.Memantine (25 µmol/kg) was administered intraperitoneally to 6 C57BL/6 mice 30 minutes before ischemia. Seven additional mice received no injection (controls). NO production and hydroxyl radical metabolism were continuously monitored using bilateral striatal microdialysis in vivo. Hydroxyl radical formation was monitored using the salicylate trapping method. Forebrain ischemia was produced in all mice by occluding the common carotid artery bilaterally for 10 minutes. Levels of the NO metabolites nitrite (NOThe regional cerebral blood flow was significantly higher in the memantine group than in the control group after reperfusion. Furthermore, the level of 2,3-dihydroxybenzoic acid was significantly lower in the memantine group than in the control group during ischemia and reperfusion. Levels of NOThese data suggest that memantine exerts partially neuroprotective effects against cerebral ischemic injury.