Acute administration of ethanol reportedly decreases total sialic acid in brain. Here, we tested the hypothesis in brain and liver that the decrement is due to increased hydrolysis of sialoglycoconjugates. Mouse tissue slices were pulse-labeled with N-[3H]acetyl-D-mannosamine, the precursor of sialic acid. Incorporation was linear for up to 4 hr of incubation. When the labeled slices were incubated with three concentrations of ethanol (0.1, 0.5, and 1 M) for 5 hr, labeled liver sialoconjugates were significantly affected only at 0.5 and 1 M ethanol, whereas labeled brain sialoconjugates were markedly decreased even at 100 mM ethanol. Sialidase activity decreased steadily with increasing concentration of ethanol, indicating that the increased hydrolysis was not attributable to an enhanced sialidase activity. n-Propanol and t-butanol had the same degradative effect as ethanol on sialocompounds; and 3 mM pyrazole, an inhibitor of alcohol dehydrogenase (ADH), had no effect on ethanol-induced degradation of sialocompounds. The protein/DNA ratio in liver showed a steady decrease with increasing ethanol. The data thus confirm the in vivo reports of ethanol-enhanced cleavage and rule out any increase in sialidase activity as a major cause.