Department of Applied Chemistry, Z. H. College of Engineering & Technology, Aligarh Muslim University, Aligarh-202 002, India Manuscript received 3 April 1996, revised 17 July 1999, accepted 22 July 1999 Adsorption of carbaryl (insecticide) has been studied on soils (untreated) and soils free of organic matter (O.M.). Freundlich and Langmuir equations are used to characterise the isotherms. Simple correlation analysis shows the significant influence of organic matter on the adsorption of carbaryl by untreated soils. In case of O.M.-free soils, adsorption is found to be correlated with the clay content and specific surface area. The clay content of the soil (O.M.-free) accounts for a very large proportion of the variation in adsorption (k value). Exothermic nature of adsorption illustrates its temperature-dependence. Evaluation of thermodynamic parameters indicates the physical nature of adsorption.