1. Four previously proposed methods of calculating the differential entropies and heats of adsorption on the basis of one adsorption isotherm were compared, and their possibilities and limits of applicability were discussed. 2. A new thermodynamic method of approximate calculation of the differential heats and entropies of adsorption according to one isotherm, based on the selection of the gas phase at a pressure equal to the product of the degree of filling of the adsorption volume by the saturated vapor pressure as the standard state, and on neglecting one of the factors in the expression for the entropy, the value of which is usually small, was proposed. It was shown for a number of examples that this method is applicable both to microporous and to nonporous adsorbents in the entire region of filling of the adsorption space. Especially good results of calculation of the heats of adsorption are obtained for systems in which the heat decreases with the filling.