Malathion (O,O-dimmethyl phosphorodithioate of diethyl mercaptosuccinate), an organophosphorus insecticide, markedly inhibited the root growth of germinating wheat seeds (4 day old) at 200 ppm. The contents of protein and DNA diminished but the RNA content increased appreciably in malathion (200 ppm) treated roots. The activity of protease was significantly inhibited but the activities of nucleases were stimulated in wheat roots on exposure to 200 ppm of malathion. The phytase activity of endosperm decreased with a decline in the level of inorganic phosphate in roots in malathion exposed condition. The activities of acid and alkaline phosphatases and ATPase increased in roots of four-day-old germinating wheat seeds on application of toxic dose of malathion.