Experimental data of the enthalpies of dilution of aqueous polyelectrolyte solutions with water are presented, as well as the exchange enthalpies of polyelectrolyte counterions. Measurements were performed using a titration calorimeter. The procedure of obtaining exchange enthalpies is described. The knowledge of these exchange enthalpies reveals information about the enthalpies of formation of (polycation-polyanion) complexes which are the basic materials for the preparation of pervaporation membranes. The data obtained are also of interest for paper manufacturing industries because they provide a model of the interaction energies of polyelectrolytes with multiple-charged electrolytes, e.g. lignin sulfonate.