Hydrogen gas significantly decreased levels of hepatic MDA, a marker of oxidative stress. Mice (n = 6 each group) were subjected to I/R with or without hydrogen gas. Ischemic livers were removed and homogenized in the presence of butylated hydroxytoluene. After centrifugation, free MDA in the supernatant was determined. Mice (n = 6) treated with helium gas (4%) instead of hydrogen gas and normal mice (without any treatment; n = 6) were also analyzed. Free MDA levels were normalized against protein contents in supernatants. The mean is presented with the standard deviation. Statistical analysis was performed using one-way ANOVA. **P < 0.0001, compared with 0% H2 gas.