(Na+,K+)ATPase activity in synaptic membranes from whole brains of mice was inhibited by a series of short-chain aliphatic alcohols (ethanol through pentanol). The relationship of inhibitory potency to alcohol chain length and to alcohol membrane:water partition coefficient suggested that the inhibitory effect of the alcohols does not depend totally on their interaction with neuronal membrane lipids. Although partitioning into the membranes is important for this inhibitory effect, a direct interaction of alcohol with the enzyme protein may also be involved in the inhibition. Norepinephrine did not significantly potentiate inhibition of (Na+,K+)ATPase activity by low concentrations of ethanol in preparations of either mouse or rat brain. Thus, under our conditions, ethanol, at levels which can be reached in vivo, only slightly inhibited enzyme activity, and the possible importance of this inhibition in mediating the in vivo acute or chronic effects of ethanol on the CNS remains open to question.