Fenclorim counteracts phytotoxic effects of the herbicide pretilachlor to rice but renders no protection to the weed species barnyardgrass. Our data suggest that the antidotal efficiency of fenclorim is due to its ability to increase the levels of glutathione and of the enzyme glutathione S-transferase in rice (but not in barnyardgrass) thereby enhancing the capacity of the crop plant to detoxify the herbicide via glutathione conjugation.