OBJECTIVE To study the effects of rapid eye movement sleep (REMS) deprivation on the expression of mRNA coding for neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) of hypothalamus in rats. METHODS Flower pot technique was adopted to deprive the REMS of Sprague-Dawley rats for 24 h, 48 h and 72 h respectively. The expression of mRNA coding for nNOS or iNOS of hypothalamus in rats was assayed by reverse-transcription polymerase chain reaction (RT-PCR). RESULTS The amount of nNOS mRNA was significantly higher in 24 h REMS deprivation group (P<0.01), then the amount was lowered in 48 h deprivation group and became significantly lower in 72 h deprivation group than that in the control group (P<0.05). There was low expression of iNOS mRNA of hypothalamus in rats, and there was no difference in the expression of iNOS mRNA among 24 h, 48 h REMS deprivation and the control groups. But the expression was significantly increased in 72 h REMS deprivation group (P<0.01). CONCLUSIONS Deprivation of REMS increased the expression of nNOS and iNOS mRNA of hypothalamus. Excessive nitric oxide (NO) might be a major factor resulting in not only the sleep rebound phenomenon but also the injury of human function caused by sleep loss directly or indirectly by other sleep factors.