Determination of CSF lactate levels were performed in 150 nonasphyxiated and 46 asphyxiated high risk neonates. Statistical analysis of log lactate levels of nonasphyxiated infants showed significant relationship to gestational and postnatal ages (P <.0001 and <.0002, respectively). CSF lactate elevation was seen in 16/29 infants studied within eight hours of asphyxia in contrast to 0/17 infants studied after eight hours (P <.001). Higher incidence of CSF lactate elevation was seen in term infants (7/8), infants with fetal distress (13/17), and very low Apgar scores (11/18). Seven of eight infants with markedly elevated lactate levels had both fetal distress and very low Apgar scores. CSF lactate determination in the immediate postasphyxial period appears to be an objective way of assessing the severity of cerebral hypoxia.