Superoxide dismutases are enzymes that catalyze the dismutation of superoxide radicals into oxygen and hydrogen peroxide. In eukaryotic cells two forms of SOD are found, one containing copper and zinc (CuZnSOD) in the cytosol and one containing manganese (MnSOD) in the mitochondria1 matrix. Inefficient detoxification of superoxide radicals has been associated with the etiology of various diseases in adults and premature infants (1 -3). Studies in several experimental animal models, including sheep, have shown that antiox !ant enzymes are weakly expressed in fetal lung until late in gestation. It has been suggested that infants born prematurely would be at increased risk for oxidative stress because of the reduced levels of lung antioxidant activity (4-6).