The authors used assessment of lactic dehydrogenase activity in cerebrospinal fluid to evaluate the severity of hypoxic damage of the CNS of neonates. The highest activity was recorded in infants who died in conjunction with the hypoxic lesion of the CNS. The lowest activity was found in neonates with a permanently normal neurological finding during infancy. From the results ensues the prognostic importance of the above examination for subsequent psychomotor development of children.