The farmer has been one of the major beneficiaries of the chemical revolution that has occurred over the past half century. The development of new fertilizers, pesticides, herbicides, fungicides and other agricultural chemicals has dramatically increased crop yields and reduced crop losses due to insects and disease. Agrochemicals, however, frequently have hidden costs that may not become apparent for years after they have been introduced on the market. Hazards to human health in the form of acute and delayed neurotoxicity resulting from pesticide exposure are the hidden costs that will be addressed in the paper. A brief review of the acute and delayed neurotoxicity of organophosphorus pesticides will be used to focus attention on the importance of neurobehavioral evaluations. Specific testing methods appropriate for the health assessment of agricultural workers will then be reviewed.