In humans, ingested alcohol is mainly metabolized by the combination of class I alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). In Orientals, there are highly frequent polymorphisms both in the class I ADH beta subunit (ADH2) and in the low Km ALDH (ALDH2). We characterized the three genotypes of ALDH2 in a Japanese population. In the present study, we evaluated the effects of the ADH2 polymorphism in the same population (424 males and 100 females) controlling for the effects of the ALDH2 polymorphism. In the ALDH2(1)/ALDH2(2) group, the frequency of facial flushing with one glass of beer was significantly higher in the ADH2(1)/ADH2(2) and ADH2(2)/ADH2(2) genotype than in the ADH2(1)/ADH2(1) genotype. Likewise, the proportion of persons with positive results for ethanol-induced cutaneous erythema differed significantly depending on the ADH2 genotype in both the ALDH2(1)/ALDH2(1) and ALDH2(1)/ALDH2(2) genotypes. However, drinking habits were not significantly associated with the ADH2 genotype, suggesting that the ADH2 genotype influences the metabolism of ethanol only in the peripheral tissues.