The effect of pre- and postnatal lead ingestion on choline acetyltransferase (ChAT) activity, muscarinic cholinergic receptors (mACHR) and on nest odor preference, was investigated in the early postnatal male rat. Long Evans dams were given either 0.15% [LL = low lead] or 0.25% [ML = moderate lead] lead acetate (controls, 0.125% or 0.075% sodium acetate) in their drinking solution from the first day of pregnancy and during lactation. Mean blood lead levels were 55 micrograms/100ml at postnatal day [PN] 6 in ML-treated offspring and 35 micrograms/100ml at PN 9 in LL-treated pups. General health of pups and dams was not affected. Lead-treated offspring showed a reduced preference for or ability to identify the smell of home bedding, when tested at PN 9. A decrease in binding (Bmax) of [3H]N-methyl- scopolamine (NMS) was detected in olfactory bulb and in visual cortex of LL-treated rats at PN 9; the affinity (KD) was unchanged. On the other hand, ChAT-activity of ML-treated offspring was significantly increased in olfactory bulb at PN 6. These results suggest that stage-specific behaviors depending on sensory functions and cholinergic projection systems in related brain areas are sensitive to pre- and postnatal lead exposure.