Newborn males are more sensitive to brain injury than newborn females are. The aim of the present study was to find an explanation for this. We used the neuron-specific enolase (NSE) levels in the cerebrospinal fluid (CSF) for the classification of 32 newborns (19 males and 13 females) on their fifth postnatal day. The NSE levels were higher than normal (8.4 +/- 1.6 ng/mL) in 10 newborn males and 6 females and were, respectively, considered asphyxiated male and female groups. The remaining newborns, 9 males and 7 females, had normal CSF levels of NSE and were considered normal newborn male and female groups. The CSF samples were measured for 12 cytokines, using a cytokine array kit, and for total hydroperoxide and biological antioxidant potentials (BAPs), using the free radical analytic system. Among the 12 cytokines measured, only interleukin 8 (IL-8) was properly detected. The CSF levels of IL-8 were higher in the asphyxiated newborn females than in the other three groups. The mean CSF levels of BAPs in the asphyxiated newborn females were higher compared with the other three groups, but significance was detected only in comparison with the BAP levels in the CSF samples of the normal newborn males. There were no differences in total hydroperoxide levels among the groups. There are sex-related differences in the CSF levels of IL-8 and antioxidants in asphyxiated newborns, with higher levels in newborn females; this might contribute in the sexual dimorphism regarding the fact that females have better protection from brain injury than the males.