The binding of fluorodifen, fenarimol, acifluorfen, 2,4-DES, methyl parathion, paraquat and pyrazophos by alpha, mu and pi class glutathione transferases (GST) was determined by the 2-p-toluidinylnaphthalene-6-sulphonate (TNS) binding fluorescence inhibition technique. Although all the 3 GST classes appear to be capable of binding the pesticides investigated, mu class exhibited somewhat higher affinity than the alpha and pi classes.