Moisture sorption isotherms of grapes, apricots, apples and potatoes were determined at 30degreesC, 45degreesC, and 60degreesC using the standard, static-gravimetric method. Six two-parameter and five three-parameter sorption models were tested to fit the experimental data. A nonlinear regression analysis method was used to evaluate the constants of the sorption equations. The Halsey equation gave the best fit to the experimental sorption data for all materials tested over the range of temperatures and water activities investigated. The GAB model gave also the closest fit to the sorption data for potatoes and grapes. The agreement between experimental and predicted values of these models was found to be satisfactory. The isosteric heat of desorption and adsorption of water determined from the equilibrium data using the Clausius-Clapeyron equation. (C) 2003 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.