A set of inhibitors that are useful for distinction of three types of human cytosolic glutathione transferase is presented. The near-neutral transferase is inhibited most effectively by Cibacron blue (I50 = 0.05 microM), the acidic transferase by Cibacron blue (I50 = 0.5 microM), and the basic transferase by tributyltin acetate (I50 = 0.1 microM). The use of any of these two compounds makes possible differentiation between all three types of human transferase.