To study the dose-dependence of the effect of alcohol on cell proliferation and nitric oxide synthase expression, rats were first divided into the control group, the 0.5 g/kg alcohol-treated group, the 1 g/kg alcohol-treated group, the 2 g/kg alcohol-treated group, and the 4 g/kg alcohol-treated group. To study the duration-dependence of this effect, animals were divided into the control, the 1-day-alcohol-treated group, the 3-days-alcohol-treated group, and the 6-days alcohol-treated group; 2 g/kg of alcohol was applied to rats over the respective number of days. Alcohol injection reduced the number of both 5-bromo-2'-deoxyuridine-positive and nicotinamide adenine dinucleotide phosphate-diaphorase-positive cells in the dentate gyrus of rats in a dose- and duration-dependent manner. These results suggest that alcohol-induced impairment in memory is due to the inhibition of new cell formation, and it is possible that nitric oxide, its synthesis is affected adversely by alcohol, plays an important role in the regulation of cell proliferation.