Basic information is given on pesticides. The chapter is divided into five major groups corresponding to their principal use: insecticides, rodenticides, fungicides, herbicides, and fumigants. The insecticides are further categorized according to chemical configuration into chlorinated hydrocarbons, phosphate esters, and miscellaneous insecticides. The pesticide solvents are not included. No attempt is made to present the clinical effects of all pesticides currently used. As far as the information is available, the threshold limit value, physiological effects, route of entry into the organism, symptoms, and diagnosis are given for the compounds considered. Those at occupational risk include manufacturers, spray pilots, crop workers, farmers, nursery workers, seed-treaters, soil fumigators, exterminators, and others engaged in the development, manufacture, distribution, and use of these chemicals. Nonoccupational activities such as gardening, yard maintenance, and camping also involve risk of exposure.