Consideration and comparison of specific superoxide dismutase activities shows that - of the values calculated for the same wet weight - the superoxide dismutase activity of the liver is more than twice that of the other tissues. This indicates the important metabolism-directing role of the liver. The large amount of superoxide dismutase (even the tissular superoxide dismutase alone) protects the tissues from the effects of the 0(2-) radical, and the function of the superoxide dismutase probably opposing the cytochrome P-450 may be important as regards the hydroxylase effect.