Allelic differences at the alcohol dehydrogenase (ADH) and aldehyde dehydrogenase loci may have an important role in an individual's alcohol sensitivity. We have cloned and sequenced all nine exons of an ADH2(2) allele which codes for an 'atypical' ADH, ADH beta 2. Our sequence data shows that the histidine at residue 47 of ADH beta 2 is encoded by CAC. Surprisingly, no silent substitution was found between the coding regions of ADH2(1) [Duester, G., Smith, M., Bilanchone, V. & Hatfield, G. W. (1986) J. Biol. Chem. 261, 2027-2033.] and ADH2(2) alleles over the 1122 nucleotide sites.