During the falling rate period of drying the heat requirements for drying hygroscopic materials may be increased substantially ahove the normal latent heat by the heat of desorption of water. In various new high intensity drying processes which are of increasing interest industrially, the drying material may reach quite high temperatures for periods of time sufficiently short that there is no degradation of the properties of the dried material. However the limited stability of many materials at high temperatures precludes determination of heals of desorption by direct measurements because of the long experimental times required for thermodynamic techniques. The present study develops a thermodymically valid method whereby heats of desorption determined at low lemperatures may be extrapolated reliably to the high temperatures where such information is needed but cannot be measured. A relation between isosteric heat of desorption and latent heat of water is derived in order to compare the new