A partial cDNA clone of the glutathione S-transferase 3 gene (GST3) was obtained by screening a lambda gt11 human lung cDNA library with antiserum to human lung GST3. The sequence of this cDNA showed two base differences from the coding sequence of a GST3 cDNA isolated from a human placental cDNA library. Hybridization of the cloned GST3 cDNA to human chromosomes resulted in a primary peak of grains over band 11q13, a localization predicted by prior experiments. An unexpected strong secondary peak of grains was obtained over bands 12q13 and 12q14, indicating that there is a GST3-like gene on the long arm of chromosome 12 in man.