: Interfacial polymerization microcapsulation processes based on isocyanate or aminoplast chemistry, where all wall-forming reactants are placed in the dispersed oil phase are described. Emphasis is placed on mechanism of interfacial reactions, physical nature of the resulting membranes and methods used to vary membrane permeability.Pesticide microcapsule formulations can be used to reduce mammalian toxicity and extend activity, to control evaporation, to reduce phytotoxicity, to protect pesticide from rapid environmental degradation, to reduce leaching and to reduce pesticide levels in the environment. Examples are provided to demonstrate how pesticide performance characteristics can be altered using this type of formulation.1998 Society of Chemical Industry ( Pestic. Sci., 54, 394È400 (1998)