H2 inhalation reduced ischemic damage and hemorrhagic volume after transient middle crebral artery occlusion (MCAO) ischemia.(19) Free radical generation after ischemia induces matrix metalloproteinase (MMP) expression.(19,20) MMP-9 promotes hemorrhagic infarction by disrupting cerebral vessels.(20) H2 inhalation has been found to reduce MMP-9 expression in an MCAO rat model. This evidence concerns the gene MMP9 and ischemia.