Objective To elucidate the role of cNOS mRNA expression in the pathogenesis of hypoxic brain injury after neonatal hypoxia. Methods RT PCR was used to measure cNOS mRNA gene expression in brain cells obtained from a neonatal rat model of hypoxia (n=25). Results The expression of cNOS mRNA in both 1 and 4 hour hypoxic groups was both increased compared with that in the control group (P<0.01), but it was decreased in the 4 hour group compared with the 1 hour group (P<0.01). Conclusions NO synthesized by cNOS mRNA in the early hypoxic phase might have some protective effect on hypoxic brain tissues.