The expression of glutathione transferase isoenzymes has been studied during the development of Bufo bufo embryo. By analysing the GSH-affinity purified materials in terms of substrate specificities, SDS-PAGE pattern, HPLC elution profile, we conclude that, up to stage 22, no significant changes in the expression of glutathione transferases isoenzymes occurred during Bufo bufo embryo development. At stage 25 the distribution of glutathione transferases was found to be slightly different from those of all other foregoing stages. A marked decrease of embryonic glutathione transferases subunits with a parallel appearance of new structurally and immunologically different subunits was noted in toad liver and kidney. Toad ovary continued to express embryonic glutathione transferase subunits.