This study was done to determine the effects of hypothermia on brain cell membrane function and energy metabolism after transient hypoxia-ischemia (HI) in the newborn piglet. Cerebral HI was induced by temporarily complete occlusion of bilateral common carotid arteries with surgical clips and simultaneous breathing with 8% oxygen for 30 min, followed by release of carotid occlusion and normoxic ventilation for 4 hr. Rectal temperature was maintained between 38.0 and 39.0 ℃ in normothermic groups, and between 34.0 and 35.0 ℃ in hypothermic groups for 4 hr after HI. During HI, heart rate, glucose and lactate level in the blood and cerebrospinal fluid increased, and base excess, pH and blood pressure decreased significantly in both normothermic and hypothermic groups. After HI, these abnormalities returned to normal in normothermic group, but lactic acidosis persisted in hypothermic group. Decreased cerebral Na⁺,K⁺- ATPase activity and increased lipid peroxidation products, indicative of HI- induced brain injury, were more profound in hypothermic group than in normothermic group. Brain ATP and phosphocreatine levels were not different between normothermic and hypothermic groups. In summary, hypothermia applied immediately after HI for 4 hr did not improve the recovery of brain cell membrane function and energy metabolism in the newborn piglet.