Simulated spillage of emulsifiable concentrate (E.C.) and microencapsulated formulations of methyl parathion on soil were studied. Persistence of residues from both formulations spilled as concentrates and as simulated from rinses were followed for up to 45 months. Spillage of encapsulated formulation resulted in the formulation of a solid cake-like deposit on the soil surface, which could be a particularly attractive hazard to small children. At 45 months, soil residues had decreased by 64% for emulsifiable concentrate spills, and 68% for the soil beneath the microencapsulated cake. Residue in the cake itself only decreased by 31%. Soil residue levels from simulated drum rinses were essentially innocuous by 45 months for the emulsifiable concentrate and by one year for the microencapsulated material. The leaching of methyl parathion from the microencapsulated cake into soil and the relationship between available residue and wet weather were also investigated.