In this study, we have isolated and characterized a gene and cDNA encoding a mouse Theta class GST. The gene, mGSTT2, spans approximately 3.1 kb and is composed of five exons interrupted by four introns. The gene was localized to Chromosome 10B5-C1 by in situ hybridization. Southern blot analysis of mouse genomic DNA suggests that there is only one copy of mGSTT2 in the mouse genome. The cDNA derived from mGSTT2 was isolated from a mouse liver cDNA library and has an open reading frame of 732 bp encoding a peptide of 244 amino acids with a calculated molecular weight of 26,676 Da. The encoded protein shares amino acid sequence identities of 92, 77, 51, and 55% with rat subunit Yrs, human subunit GSTT2, rat subunit 5, and human subunit GSTT1, respectively.