Increasingly widespread application of organophosphate pesticies has underscored the importance of studying their effects on human behavior. Clinical reports and laboratory investigations have generally supported the assumption that neurobehavioral manifestations of organophosphate toxicity are attributable to accumulation of acetylcholine at central and peripheral synapses as a result of cholinesterase inhibition. Despite methodologic shortcomings in many of the published studies, investigators generally agree on the presence of several behavioral sequelae of organophosphate poisoning: (a) impaired vigilance and reduced concentration, (b) slowing of information processing and psychomotor speed, (c) memory deficit, (d) linguistic disturbance, (e) depression, and (f) anxiety and irritability. The few studies of asymptomatic workers at risk for repeated exposure to organophosphate pesticides have produced only equivocal findings concerning the presence of less severe or latent forms of these behavioral abnormalities.