During a six-month period, lactate measurements were performed on all samples of CSF obtained by lumbar puncture from infants of varying gestational ages between birth and 32 days of age. The normal levels of lactate in the CSF of newborns were demonstrated to be higher than those previously reported in older children or adults. A steady decrease in CSF lactate levels was demonstrated as postnatal age increased, so that after the first ten days of life, CSF lactate levels were within the range reported for older children and adults. We could not demonstrate that neonatal asphyxia or gestational age significantly altered these values.