The study demonstrated that pH and oxidation-reduction conditions affect the persistence of pesticide compounds and that different compounds may respond differently to a given physicochemical environment. The stability of kepone was little affected by altered pH and oxidation conditions, DDT was markedly affected by oxidation conditions, and the degradation of permethrin was strongly influenced by both pH and redox potential conditions. The mechanism by which pH or redox potential affected the degradation of two of the three pesticides studied was not determined. It could have involved purely chemical processes. The effect also could be secondary through the influence of physicochemical conditions on the population and activity of microorganisms present and the subsequent metabolic action of these microbes on the compounds. A combination of these processes also could have been involved. Information on the effects of physicochemical conditions on the adsorption and degradation of specific pesticides should contribute to improved predictive capability concerning the fate of pesticide residues in various compartments of the environment.