In studying the potential health hazards associated with the use of pesticides, three segments of the population should be considered. These segments include: (1) The formulator or sprayman who mixes and/or sprays the chemicals and has a relatively high degree of exposure. (2) The so-called 'innocent by-stander' who has no intentional exposure but who may be inadvertently exposed when dust or spray drifts onto his home during application to adjacent fields or orchards. The child who innocently plays with a supposedly empty insecticide container, or who eats or drinks a pesticide from an unlabelled bottle, also may be considered in this category. (3) The general population, all of whom have some degree of exposure to pesticides residue in their daily diet. Studies carried out at our laboratories have attempted to evaluate the hazard to each of these population groups from pesticide usage.