Volatilization of pesticides from treated agricultural crops constitutes a major input of these chemicals into the atmosphere. Microencapsulated pesticide formulations are designed for slow release of biocides and thus increase the residence time on the plant foliage. The rate of volatilization for these formulations should also be substantially less than that from non-encapsulated forms. Methyl parathion was applied to a field in both microencapsulated and emulsifiable concentrate forms. Air samples were taken on the downwind side of the field with a sampler which employs a composite filter designed to trap both particulate and vapor forms of organophosphorus pesticides. Air was sampled beginning 1 hr. after spraying and during intervals for 9 days after application of the insecticide. The physical form of the formulation applied to the plants had a profound effect on the levels of airborne pesticides found near the field.