Although Drosophila simulans is closely related to D. melanogaster, very fewcytochrome P450 genes have been studied in this species until now. As Cyp6a2 from D.melanogaster is a major gene implicated in the detoxification of xenobiotic molecules, wedecided to look for its ortholog in D. simulans. The isolated gene, Cyp6a26, presentsstructural characteristics very similar to those of Cyp6a2: an identical size of 1590-bpcomprising two exons separated by a 69-bp intron and a nucleotide sequence homology of95%. Many putative transcriptionally important motifs were identified in the upstreamDNAs of the two genes but only 16 elements are in common positions. Treatment of flies withphenobarbital leads to an increased production of Cyp6a26 mRNAs. The expression ofCyp6a26 mRNAs varies following developmental stages in the same manner as Cyp6a2.Immunohistochemistry experiments of phenobarbital-treated adult drosophila show that thespatial expression patte of the two proteins is also conserved between the two species. Allthese data argue in favor of the conservation of the function of these homologous genesbetween the two Drosophila species.