Two commercial magnesium stearate powders in two well-characterised structural states are investigated using DSC and coupled TGA-DTA under dry nitrogen flow. They consist of either a mixture of crystalline hydrates or a poorly crystallised so-called anhydrate. Following the degassing of unbound water, 1 or 3 weight-loss peaks are observed below about 100 degrees C, each associated with one heat loss peak at the same temperature. The present results and a review of graphical data from literature show that the so-called anhydrate always contains a significant amount of water. At the beginning of the dehydration process, the beat loss is the same as the standard heat of vaporisation of water and then gradually departs from it by positive values. The idea according to which the mixture of dihydrate and trihydrate loses water to form the anhydrate cannot be quantitatively reconciled with the present and other gravimetric results. (c) 2004 Elsevier B.V. All rights reserved.