Human livers express a variety of cytosolic glutathione S-transferase isoenzymes. The enzymes are subject to a marked polymorphism and the polypeptide basis of the differences in glutathione S-transferase content of individual livers has been investigated by Western blotting, hydroxyapatite HPLC and isoelectric focusing. Collectively, the livers examined contained three distinct groups of cytosolic glutathione S-transferase. The three classes of enzyme contain subunits of different molecular mass; subunits of 24.8 kDa (Yf), 26.0 kDa (Ya) and 26.7 kDa (Yb) were found to belong to the 'acidic-type', 'basic-type' and 'neutral-type' glutathione S-transferase, respectively. All livers studied contained 26.0 kDa subunits (Ya or 'basic') but significant differences in the isoelectric points of this group of proteins were demonstrated. Five of the eight livers examined expressed 26.7 kDa subunits (Yb or 'neutral'); the native enzymes had pI values of either 6.1 or 5.5, and were isolated by hydroxyapatite HPLC. Two of the livers possessed 24.8 kDa subunits (Yf or 'acidic'), and the native enzyme, which had a pI of 4.8, was also purified by hydroxyapatite HPLC. Before undertaking a glutathione S-transferase purification it is advisable to determine the GST isoenzyme content of a number of livers. The suitability of the methods described in the present study for use as screening procedures is discussed.