AbstractThe gene coding for alcohol dehydrogenase (Adh) in Drosophila melanogaster maps to 2:50.1 on chromosome arm 2L. It is expressed in both larvae and adults, coding for an abundant enzyme that plays a role in the detoxification of primary and secondary alcohols. In larvae the gene is most abundantly expressed in the fat body and gut. We have recently shown [49] that the major Adh transcripts differ in larvae and adults, the major adult transcript being initiated from a promotor several hundred pairs 5′ to the promotor from which the major larval transcript is initiated. However the coding region of the “larval and adult” mRNA are identical. We discuss recent studies of the transcriptional organization Adh and compare the structure of this gene in D. melanogaster with that in other species of Drosophila. The entire Adh gene and its surrounds has been sequenced from four species of Drosophila [45,48]. This data has been used not only for the study of phylogenetic relationships, but also of the types of sequence variation seen between species. The constraints on mutational change, especially with respect to codons, will be discussed.