The vapor of two volatile organic compounds, ethylbenzene, and tetrachloroethylene were adsorbed to natural and organically modified montmorillonite clays, respectively. The surface of clay was modified using a cationic surfactant, hexadecyltrimethylammonium (HDTMA) with a cation-exchange capacity of 161 mg HDTMA/g-clay. The adsorption was performed by passing the mixture of nitrogen and the vapor of organic compounds through a fixed adsorption bed. Desorption was also conducted by allowing the pure nitrogen to flow through the loaded bed. The experiments were conducted at 24, 34, and 44 degrees C in order to investigate the effect of temperature on the adsorption and desorption behavior of the two types of clays. The adsorption data were modeled with the BET adsorption isotherm equation. The isotherms of natural and modified clays exhibited a typical favorable Type I behavior. The temperature effect on the adsorption capacity was significant when the natural clay adsorbed the two organic compounds, while the temperature effect was minor when the modified clay was used. The desorption rate constants were in the order of 10(-5) min(-1) and these values were not greatly varied when the type of clay changed from natural to modified clay.