Moisture desorption isotherms of Morchella esculenta mushrooms were determined at 5. 15, 25 and 35 degreesC and within the range of 0.11-0.92 water activity using a standardized conductivity hygrometer. Five models were considered to describe isotherms (GAB, Oswin modified, Henderson modified, Halsey modified and Ratti) being fitted to the experimental data by direct non-linear regression. The GAB and Ratti equations gave the best fit of the experimental data. Isosteric heats of water desorption were obtained from the experimental data by applying the Clausius-Clapeyron equation within the range of 0,04-0.50 moisture content (dry basis). (C) 2002 Elsevier Science Ltd, All rights reserved.