We report here the initial characterization of the alcohol dehydrogenase (Adh) gene family of the allotetraploid Gossypium hirsutum, a crop plant that is highly sensitive to waterlogging. Twelve Adh cDNAs were isolated from a library constructed from RNA prepared from anaerobically stressed root tips. Nine of the twelve cDNAs fell into one class, while each of the other three cDNAs fell into a separate class. The 3'-untranslated regions had little or no homology between classes implying that each of these four classes is encoded by a different gene. The most abundant class of Adh cDNA was expressed under the control of the 35S promoter in transgenic cotton and encodes the ADH2 isozyme, the isozyme induced most strongly by low oxygen conditions. Cotton Adh genomic segments were sequenced. The promoter regions of these Adh genes contain the cis-acting motifs which have been shown in other plant species to be necessary for anaerobic induction of transcription. A gene conversion event is likely to have occurred between the 3' ends of two of the genes. Sequence comparison of the Adh genomic and cDNA clones, and Southern analysis of genomic DNA suggest the existence of multiple copies of Adh genes in cotton. Five different members of this Adh gene family of cotton have been identified, of which four are very similar.