Phylogenetic relationships and evolutionary rates for 36 alcohol dehydrogenases (ADHs) from vertebrates and plants are described, with ADHs from fission yeast and from baker's yeasts as outgroups. Vertebrate sequences include 15 mammalian, 2 avian, and 1 amphibian ADH, as well as one sequence deduced from a human pseudogene. Plant ADH sequences include 1 from a gymnosperm (loblolly pine) and 16 from angiosperms, in which 9 sequences are from monocots and 7 are from dicots. Phylogenetic analysis shows that ADHs from vertebrates and from plants are classified into two distinct groups, and the latter group is further divided into angiosperm and gymnosperm ADHs. Among three classes of vertebrate ADHs, class I and II ADHs are most closely related and evolved at much faster rates than did class III ADHs. The gymnosperm ADH has evolved more slowly than any angiosperm ADH. However, ADHs within both of the vertebrate classes I and II and class III groups have similar evolutionary rates, as do most of the ADHs within the angiosperm group. The rate of amino acid replacement for the vertebrate and plant ADHs is approximately 0.3-0.6 x 10(-9)/site/year.