The equilibrium exchange of alkali metal ions (Li+, Na+, K+ and Cs+)/H+ system has been studied in MCl-HCl media at 25, 40 and 60 degrees C. The exchange isotherms have been measured for both forward and reverse reactions, at a solution ionic strength of 0.1, by the batch technique. On the basis of the exchange isotherms, thermodynamic parameters have been calculated and some predictions made for the exchange process taking place in the materials. The selectivity sequence shows that K+ < Na+ < Li+ < Cs+.