Feeding human milk reduces the risk of developing necrotizing enterocolitis(NEC) in the low birth weight infant. This may be related to the many antioxidant properties of human milk, since NEC may be induced by excess superoxide radicals in the intestine (Saugstad, Acta Ped Scand 1990:79,88). Human milk contains superoxide dismutase (SOD) as well as other antioxidant proteins that are not present in cows' milk based formulas (F). We hypothesize that HM has superior antioxidant properties when compared to F, with and without normalization of the Vitamin C levels in HM to those levels in F. To test this hypothesis we induced physiological oxidative stress in HM (n=5) and F (n=2) to produce superoxide radical by the addition of 500 micromolar hypoxanthine and 25mU/ml xanthine oxidase to HM and F. Ascorbate radical(Asc·-) was measured using electron paramagnetic resonance spectrometry(EPR) and O2 consumption (O2C) using a YSI oxygen probe. Preliminary results indicate (1) that during oxidative stress, Asc·- is formed less in HM then in F. (2) Asc·- production is more intense in F compared to HM with and without oxidative stress. (3) O2C in HM is less than that in F with and without oxidative stress. These finding suggest that HM SOD may be a factor in protecting against NEC and HM undergo less oxidation with and without oxidative stress than F.