Eight dimeric isoenzymes of glutathione S-transferase (GST) were purified from liver, kidney and testis of the Syrian golden hamster, using S-hexylglutathione affinity chromatography and chromatofocusing. The isoenzymes were characterized according to their substrate selectivity, physical properties and amino acid sequence analysis. Thus a classification into Alpha, Mu and Pi classes was made in analogy with GSTs of other species. Two Alpha-class GSTs were purified, termed A1A1 (pI 8.9) and A1A2 (pI 8.6). Four Mu-class subunits were detected (M1-M4), all forming homodimers, with M2 and M3 also forming a heterodimer. The isoelectric points ranged from 5.9 to 8.6. One Pi-class isoenzyme was purified and termed P1P1 (pI 6.8). Using h.p.l.c. analysis, the subunit composition was determined in a number of organs. The major subunits in liver were A1 and M1. Subunit A1 was also the major subunit in the kidney. Subunit M1 was not detected in kidney, while subunit P1 was not found in the liver. Pancreas and trachea contained predominantly the Pi-class subunit, P1. GST in the testis was mostly of the Mu class. The major subunit was M4, and subunits M2 and M3 were exclusively detected in the testis.