Abstract. Lead (Pb) at the dose of 0.2% (w/v) containing 1100 ppm of Pb was given to female Swiss-Webster strain mice in their drinking water. Treatment started from the first day of pregnancy until the day of delivery. Thereafter, the dams were switched to plain tap water. The control as well as the treated mothers and offspring were cross-fostered on first day of delivery in a way that four groups were created, viz : control mothers v/s control pups (Cm-Cp); control mothers v/s treated pups (Cm-Lp); treated mothers v/s control pups (Lm-Cp) and treated mothers v/s treated pups (Lm-Lp). All cross-fostered offspring were subjected to various tests. The affected parameters were a decline in the body weight gain, delayed opening of the eyes and retarded development of the sensory motor reflexes in the pups throughout their postnatal developing weaning period. Alterations were noticed in the levels of acid and alkaline phosphatases in liver, and acetylcholinesterase in the brain tissues of the developing offspring. Significant increase in various parameters of 'locomotory test', and a significant decrease in attacking behaviour and alteration in the acts and postural behaviour in the ‘Standard Opponent Test’ was observed in the Pb exposed adult male offspring. The 'tube restraint test' showed a significant change in the latency to the first bite and in the number of target biting by the Pb exposed female offspring. Overall observations on behavioural and biochemical parameters showed a significant effect of Pb in the cross-fostered offspring in the order of Lm-Lp > Lm-Cp > Cm-Lp as compared to the control (Cm-Cp). The present Pb effects in cross-fostered offspring are possibly via in utero action and/or via mother’s milk.