The equilibrium studies have been made on different types of cation exchangers in hydrogen form with univalent alkali metal ions. It has boon concluded that the apparent equilibrium constant (Ka) varies irregu­larly with the concentration of the external solution and hence with the equivalent fraction of the ion in the resin phase (XBR) in all the cases. The shape of the curves for plots of Ka versus XBR differs from resin to resin, leading to different maxima in different cases.