Our previous studies indicated that inhibition or ablation of the neuronal nitric oxide synthase (nNOS) prevents the development of sensitization to the locomotor-stimulating effect of cocaine and cocaine-induced conditioned place preference (CPP). The present study was undertaken to investigate the effect of the nNOS inhibitor, 7-nitroindazole (7-NI), on ethanol-induced locomotor sensitization and CPP in DBA/2J mice. Administration of ethanol (1.5 g/kg; i.p.) for 7 days resulted in a progressive increase in the locomotor-stimulating effect of ethanol. Pretreatment with 7-NI (25 mg/kg) blocked the expression of the sensitized response to ethanol. A challenge injection of ethanol given 1 week and then 4 weeks following withdrawal from ethanol indicated that (a) ethanol sensitization was long lasting, and (b) the co-administration of 7-NI and ethanol attenuated the sensitized response to ethanol challenge. The CPP experiments showed that pairing four ethanol (2.5 g/kg) injections with a specific environment resulted in a marked preference for the drug-paired environment. The pretreatment with 7-NI (25 mg/kg) completely blocked ethanol-induced CPP. 7-NI alone produced neither rewarding nor aversive effects. Taken together, results of the present study indicate that blockade of nNOS by 7-NI-attenuated ethanol-induced behavioral sensitization and completely blocked the rewarding effect of ethanol. These findings support the role of NO in ethanol actions and further suggest that the nNOS system is relevant to the rewarding effects of various drugs of abuse.