The incubation in deuterium-depleted medium of mitochondria isolated from the liver of rats that consumed drinking diet with depleted deuterium (46 ppm) revealed a higher (by 35%) generation of hydrogen peroxide in comparison with the mitochondria (isolated from the liver of rats that consumed drinking diet with 152 ppm deuterium) incubated in medium that contained 152 ppm deuterium. Succinate addition to the reaction system led to an increase in the production of hydrogen peroxide in isolated mitochondria by 44-81%, whereas the difference in the generation of H2O2 between the organelles incubated in mediums 46 and 152 ppm was reduced by 14%. The revealed change in the functional activity of mitochondria suggests the ability of the organism to adapt to the deuterium-depleted drinking diet, which is probably due to the formation of the D/H isotope transmembrane gradient.