Persons who have the Glu-487-->Lys mutation (single nucleotide polymorphism) of the aldehyde dehydrogenase-2 (ALDH2) gene have less ability to metabolize the alcohol breakdown product acetaldehyde. In order to clarify whether acetaldehyde is associated with the pathogenesis of alcoholic polyneuropathy, we compared nerve conduction data as well as clinical signs and symptoms of neuropathy between alcoholics with ALDH2*2 (Lys-487) heterozygotes and those with ALDH2*1 (Glu-487) homozygotes. Alcoholics with ALDH2*2 heterozygotes showed significantly lower sensory nerve action potential amplitudes of the sural and median nerves than those with ALDH2*1 homozygotes, suggesting that the accumulation of acetaldehyde due to ALDH2 inactivity is associated with alcoholic polyneuropathy.