DDT, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane is one of the best-known insecticides which produces neurotoxic syndrome in mammals. DDT is also a world-wide environmental contaminant which is still used in several countries. We have previously reported on pronounced retention of DDT in the neonatal mouse brain. We have also observed that DDT and a DDT metabolite, DDOH, conjugated to palmitic acid (DDOH-PA), which have been found in DDT-treated female rats, affect the muscarinic cholinergic receptors in the brain of the neonatal mouse. We now report that neonatal exposure to a single low oral dose of DDT and DDOH-PA (1.4 mumol/kg b.wt.) also can lead to a permanent hyperactive condition in the mice as adults.