A new experimental technique is described for the determination of desorption characteristics for engineering purposes. A TGA-DSC setup is used in isothermal mode to achieve the thermal desorption of deformable standard materials like microcrystalline cellulose and kaolin in dry air. Assumptions on heat and mass transfer are made and discussed in order to derive desorption isotherms and heat of sorptions from the calorimetric and gravimetric signals. The method is rapid and accurate for high-temperature desorption processes T ¿ 40 • C. It is particularly reliable for small water activity values 0 6 aw 6 0:4 where a good agreement with standard methods is observed in spite of small apparent diusion coecients D ∼ = 10 −10 m 2 s −1 for the two products tested. The method is suitable for heat sensitive biological products because of the small residence time in the furnace (1 or 2 h).