Levels of lactic dehydrogenase (LDH) in the cerebrospinal fluid (CSF) have been used to evaluate a variety of neurologic disorders. However, few studies have been performed on neonates. CSF samples were collected from 39 neonates, 19 aged 1-4 weeks and 20 aged 5-8 weeks with neonatal fever. Findings were compared to those in 15 infants mean age 10 +/- 6.4 months with suspected nervous system disease and normal CSF findings. Mean total LDH activity in the CSF was significantly higher in the first month of life than in the second month of life and compared with the control group (p <0.001). The LDH isoenzyme pattern was also different, with lower values of LDH-1 than LDH-2 and -3 in the study groups. Differences were significant among all three groups for LDH-1 (p <0.001) and between the whole study group and the controls for LDH-2 and -3 (p <0.001). We propose reference values for total LDH activity and LDH isoenzyme distribution in the CSF of normal neonates.