Comparative studies of the vaporization rate of the volatile components present in aqueous suspensions of microcapsules containing the organophosphorous insecticides S-1,2-bis (ethoxycarbonyl) ethyl-O,O-dimethyl phosphorodithioate (malathion) and O,O-diethyl S-2-ethylthioethyl phosphorodithioate (disulfoton) from inert, porous surfaces, under controlled laboratory conditions simulating natural environmental factors, were carried out. Volatilization into the atmosphere, under the given experimental conditions, was evaluated by the rate of weight loss of the microcapsule deposit and by gas chromatographic analysis of the residual insecticide on the support.