The experiments examined the relationship between behavioral alterations and neurochemical changes in rats exposed repeatedly to disulfoton, an organophosphate cholinesterase inhibitor. Male Long-Evans rats were injected ip for 30 days with 0, 0.5, 1, or 2 mg/kg of disulfoton in corn oil. Clinical signs and motor activity were measured during the course of repeated exposure. Cognitive function, as measured in the Morris water maze, and passive avoidance procedures were assessed near the end of the dosing regimen. Regional brain acetylcholinesterase (AChE) activity was measured during the course of dosing while the total number of muscarinic receptors was measured at the end of the dosing regimen. Disulfoton affected the acquisition of water maze performance, but had no effect on passive avoidance acquisition or retention. Repeated exposure to disulfoton decreased brain AChE activity and the number of (3H)quinuclidinyl benzilate binding sites.