Dimcthoate (Cygon®) decomposition was studied following the application (1 lb actual per acre) of an emulsifiable concentrate to a cultivated sandy loam soil. Half of the insecticide in the top 3 in. of soil disappeared in 4 days in drought conditions and in 2.5 days after moderate rainfall. Rate of disappearance did not change with repeat applications and rainfall did not cause appreciable leaching into the 3-6 in. zone.