The present study tests the hypothesis that rutin, a natural antioxidant, can protect brain cell membrane function during hypoxia in newborn piglets, as indicated by the preservation of Na+, K+-ATPase activity. Lipid peroxidation products and Na+, K+-ATPase activity were measured in 17 anesthetized, ventilated newborn piglets divided into 3 groups. 6 piglets served as normoxic control, 5 as placebo-pretreated hypoxic group and 6 piglets as rutin-pretreated hypoxic group. Rutin-pretreated piglets received 100 mg of rutin intravenously 30 min prior to hypoxia. Cerebral tissue oxygenation was assessed by 31P-NMR spectroscopy. Hypoxia was induced by decreasing FiO2 to achieve a 70% reduction in the phosphocreatine to inorganic phosphate ratio (PCr/Pi) compared to basal level for 1 hr. PCr/Pi was reduced from 1.53 to 0.46 in hypoxic group and 1.27 to 0.39 in rutin-pretreated group during hypoxia. Lipid peroxidation products (TBARS) increased significantly in hypoxic group compared to rutin pretreated hypoxic group (17.1 ± 1.7 vs 13.0 ± 2.2 nmoles/g brain tissue, p<0.05). Na+, K+-ATPase activity decreased significantly in both hypoxic and rutin pretreated hypoxic group compared to control group(39.3 ± 2.3, 41.4 ± 4.3 vs 51.9 ± 5.2 μ moles Pi/mg protein/hr, p<0.05), but there was no significant difference in Na+, K+-ATPase activity compared between hypoxic and rutin pretreated hypoxic group. Although this study does not demonstrate a protective effect of rutin on brain cell membrane function in vivo, rutin did decrease lipid peroxidation during cerebral hypoxia in newborn piglets in vivo. As a potent natural antioxidant, it could be used to decrease free radical effects under pathologic conditions, including cerebral hypoxia.