Malathion under in vitro condition even at lower concentration (250 ppm) altered the level of enzymes associated with glutathione cycle and antioxidant defence system in human fetal brain and liver. Such changes involved alterations in glutathione status and extent of lipid peroxidation. The inhibitory effect of malathion was dose dependent in case of human fetal brain and was more vulnerable than fetal liver. This alteration (inhibition or activation) was maximum in case of tissues from fetuses of early period of development, suggesting greater susceptibility of human fetus towards this organophosphorus insecticide.