Pesticides constitute a unique group of biologically active chemicals in that they are produced for deliberate release into the environment, usually to produce some specific biocidal effect. Workers at all stages of pesticide production and application become exposed, at least on an occasional basis, while some experience routine exposure. The general population is, in turn, exposed to the residues, in air, water and food. This review is intended to survey the present knowledge of the immunotoxicity of 20 pesticides. As will be readily seen, knowledge of pesticide immunotoxicology to date is largely descriptive with only modest beginnings toward understanding mechanisms underlying the effects. In most cases the effects have not yet to be defined in immunological state, and just as little is presently known about how these chemicals exert their effects. There is an equally great gap in perceiving any relationship between the structure of a chemical and immunotoxicological potential.