There are some reports that neuronal and inducible NOSs (nNOS, iNOS) exacerbate cerebral infarction whereas endothelial NOS (eNOS) conversely alleviates cerebral infarction in a model of middle cerebral artery (MCA) occlusion. But the role of the whole NOSs system in cerebral infarction is not clarified yet. Although it has been examined in pharmacological studied with non-selective NOS inhibitors, the results are quite inconsistent, possibly because of non-specificity of the agents. In order to investigate the role of the whole NOSs system in the pathogenesis of cerebral infarction, in the study, we generated mice in which all 3 NOS isoforms are completely disrupted, and compared cerebral infarct size after middle cerebral artery occlusion between the triple NOSs^-/- and wild-type.