The toxic effect of Malathion (50mg\100gm) Hexachlorocyclohexane (HCH) (6mg/100gm) and HCH+ Malathion (6mg HCH and 50 mg Malathion\100 gm bodyweight) on Cassava diet (65%) during the critical period of organogenesis and their consequent effect on the offspring were studied. Smaller size of the fetuses and poor ossification sites showed that cassava diet containing HCN (15.6mg/100gm food) produced maternal and embryo toxicity.The effect was marginal with respect to HCH but Malathion appeared to produce severe effect. The offspring of cassava diet fed rats had lower birth weights and pesticide exposure with the same cassava diet as their dams on subsequent mating did not conceive at all. Urinary excretion of thiocyanate was elevated and rhodanese activity in the maternal liver and placenta was considerably lower in cassava diet fed pregnant rats and pesticide exposure further magnified the activity. Cassava feeding decreased the hepatic microsomal carboxylesterase and increased the hepatic cytosolic glutathione -S- transferase. Malathion has no effect on the activity of hepatic carboxyl esterase while glutathione -S- transferase was inhibited. HCH appears to deplete the hepatic carboxyl esterase and cytosolic glutathione- S- transferase activity.