Ion-exchange equilibria are presented for Au(CN)(2)(-)/Cl-, Au(CN)(2)(-)/SCN-, and SCN-/Cl- in aqueous solution at 303 K using Purolite A500 as the ion exchanger. The effect of the total solution concentration on the ion-exchange isotherm for each binary system is considered. The experimental data are correlated using the law of mass action, modified with activity coefficients, to determine the equilibrium constant for each binary system. It is shown that the isotherm for each binary system is independent of the total solution concentration, within the range of concentration considered. The selectivity of Purolite A500 for a given ion increases in the order Cl- < SCN- < Au(CN)(2)(-). The fitted values of the equilibrium constants are in qualitative agreement with the selectivity of the resin for the various ionic species.