Behavioral consequences of low-level lead (Pb) exposure include impairments in learning processes and in Fixed-Interval schedule-controlled operant behavior. Although the neurobiological bases of these effects remain undetermined, current evidence suggests that inhibitory effects of Pb on the NMDA receptor complex may play a preferential role in the learning deficits. In contrast, alterations in dopaminergic systems, consistent with a decrease in dopamine availability, appear to be related to the changes in Fixed-Interval performance. Hypocholinergic function has also been described, but its relationship to the behavioral changes is not yet known. Explication of these relationships will require more efforts involving direct rather than correlative methods. The answers are critical for understanding risks associated with exposure and for the development of behavioral or chemical therapeutic strategies for dealing with lead neurotoxicity.