Nitric oxide (NO) has been identified as a neurotransmitter, which regulates cerebral blood flow and exhibits a neurotoxic effect during cerebral ischemia. The objective of this study was to determine the levels of nitrite(NO2-)/ nitrate (NO3-) as markers of NO production in the CSF of neonates and to correlate their concentrations with the extent of brain damage, as demonstrated by cranial ultrasonography (CUSG). CSF was obtained by lumbar puncture during the first 24 hrs of life in 42 preterm(EGA: 24-34 wks) and 5 full term babies.CUSG was done as part of clinical care. NO2- and NO3- levels were measured by fluorometric method and spectroscopy, respectively. In neonates without intracranial hemorrhage (ICH), we found total concentrations(mean±S.D.) of NO2-/ NO3- (29.6±2.7μM,n=30), which were 5-6 times higher than levels reported in adults (4-5μM), and changed nonlinearly with GA, with peak concentration at 30-31 weeks (p=.04, ANOVA). In babies with grade I-II ICH the NO2-/ NO3- levels (31±7.6 μM, n=15) were not different from those without ICH; while two babies with grade III-IV ICH had very high levels(225±152μM, p=.0001 vs no ICH). We conclude that NO production is higher in the CSF of neonates than in adults and is related to GA. Further studies are needed to elucidate the role of NO in neonatal brain damage.