The inducibility of Glutathione S-transferase (GST) in male Sprague-Dawley rats, treated with phenobarbital (PB), 3-methyl-cholanthrene (MC) and ethoxyquin (ETQ), was examined in detail. The subunit compositions of hepatic and renal GST were determined by using a reverse-phase HPLC technique. In liver, PB was found to induce the Yb1, Yb2, Ya1, Ya2 and Yk subunits by about 2.1-, 1.8-, 1.8-, 4.4- and 2-fold, respectively, while MC induced the Yb2, Yc, Ya2 and Yk subunits by about 1.5-, 1.5-, 6- and 1.7-fold, respectively, and ETQ increased the levels of Yb1, Yb2, Yc, Ya2 and Yk subunits by about 2.1-, 1.7-, 1.9-, 14.9- and 1.8-fold, respectively. In contrast, kidney cytosolic GSTs were induced only by treatment with ETQ and PB and MC had little or no effect. The Pi class subunit Yp in the rat kidney was increased about 4-fold and the Mu class Yb2 was induced by about 2-fold, by the ETQ treatment.