Moisture equilibrium data of Ch. ambrosioides leaves by desorption and adsorption were determined at 30, 40, and 50 degrees C by the gravimetric static method. The equilibrium was achieved after 12 days for desorption and 12 days for adsorption at water activities ranging from 5% to 90%. The hysteresis effect was not distinctly observed in the range of temperatures tested. Six mathematical models were used to fit the experimental data. The modified Halsey model was the best model describing the equilibrium moisture data for desorption. The GAB and modified Halsey models were the most suitable models for estimating adsorption isotherms. The net isosteric heats of sorption of water were calculated by applying the Clausius-Clapeyron equation to the sorption isotherms at different temperatures. (c) 2004 Elsevier Ltd. All rights reserved.