A wide scope of application of a novel isothermal sorption microcalorimeter is presented. With the technique, it is possible to simultaneously and independently in one experiment obtain the sorption isotherm of a sample along with the corresponding differential enthalpies of sorption. The method is suited for measurements with water vapor as well as organic vapors and has been tested at temperatures between 25 and 40 degreesC. The technique is suitable for the thermodynamic characterization of the sorption process. It is demonstrated that the method can be applied to the study of a wide range of physico-chemical phenomena associated with the uptake of vapor by a substance/material including capillary condensation, crystallization, lyotropic phase transitions and hydrate/solvate formation. The calorimetric data are reproducible and agree well with the results of well-established techniques such as solution calorimetry, differential scanning calorimetry, sorption microbalance and osmotic stress measurements.