Recently,Ohsawa et al. provide evidence that inhaled hydrogen gas has antioxidant and antiapoptotic activities that protect the brain and liver against ischemia-reperfusion injury. In fact,there is some endogenous hydrogen produced by intestinal bacteria within animal and human.The concentration of hydrogen in some mice tissues reached the antioxidant effect in their paper demonstrates,so we think that hydrogen should be an endogenous antioxidant in the body.