Screening of a genomic mouse DNA library with a glutathione S-transferase class mu cDNA probe resulted in the identification of mGSTM5, a novel member of the murine glutathione S-transferase class mu gene family. Here we present the sequence of the promoter region, the exon-intron organization of the gene and the isolation and characterization of its complete cDNA. Conceptual translation of the cDNA sequence revealed that several amino acid positions have been changed in 'invariant' mu class signature sequences in mGSTM5. Reverse transcriptase polymerase chain reaction using gene specific primers revealed that mGSTM5 is uniquely expressed in mouse liver, stomach and small intestine.