Anionic (Yb) rat liver glutathione-S-transferases are susceptible to temperature or pH dependent transitions to more basic forms of this class of proteins. At elevated temperatures (25-30 degrees) or at pH values above 9.0 the protein is rapidly and irreversibly converted to forms that are no longer retained by anion exchange resins and display basic components in chromatofocusing systems, because bound glutathione is removed at the higher temperatures or pH. Sharp increases in enzymatic activity with 1,2-dichloro-4-nitrobenzene as a substrate, accompany the temperature induced changes. Microheterogeneity patterns for this protein are contingent upon these interconversions, and the results explain apparent variations in relative amounts of the multiple forms under different conditions in terms of glutathione binding.