The homologous genomic region that contains two paralogous genes, Adh and Adh-dup, was compared in several Drosophila species. Sequences were analyzed as follows: a) At the nucleotide level, Ka and Ks values were determined for each pair of species. Ka-Adh and Ka-Adh-dup are not significantly different. However, Ks-Adh values are significantly lower than Ks-Adh-dup, which are more variable. In agreement with other reports, lower Ks values for Adh correlate with a high level of gene expression and relatively high percentage of G+C content in the third codon position, while the opposite applies to Adh-dup. b) At the protein level, amino acid comparisons reveal conserved regions shared by ADH and ADH-DUP, which have been assigned to known functional domains. Key residues for dehydrogenasic function are also found in ADH-DUP, thus pointing to a dehydrogenase activity for ADH-DUP, albeit very different from that of ADH.