We have isolated aDrosophila gene,DmGST-2, that encodes glutathioneS-transferase, a homo- or heterodimeric enzyme thought to be involved in detoxification of xenobiotics, including known carcinogens. The encoded protein has a primary sequence that is more similar to mammalian placental and nematode GSTs than that of a previously describedDrosophila GST gene, herein referred to asDmGST-1. We provide a physical map of the gene and show that it specifies at least two mRNAs, measuring 1.9 and 1.6 kb, which differ only in the lengths of their 3 untranslated regions. Both of the mRNAs are present during all developmental stages.In situ hybridization of theDmGST-2 gene to larval polytene chromosomes places it within the 53F subdivision of chromosome 2, and Southern blotting to chromosomal DNA indicates that the gene has no close relatives within theDrosophila genome. Our results make possible molecular genetic approaches for further elaborating the function of glutathioneS-transferases in insect development and physiology, in the metabolism of plant toxins, and in conferring insecticide resistance.