Department of Chemistry, Presidency College, Calcutta Received 5 January 1972 Copper and nickel complexes of Dowex A-1 chelating resin, a polystyrene-DVB matrix with iminodiacetic acid as the functional group, have been prepared by the controlled addition of Cu- and Ni- sulphate to the hydrogen form of the resin at two different temperatures. The equilibrium constants of these reactions have been calculated from the molalities of the ions present. The distribution constants have also been calculated from the amount of the ions present in both the phases. The free energy changes of these reactions have been evaluated by using both the constants, to ascertain the role of water invasion and consequent swelling of the resin. Thermodynamic constants like enthalpy and entropy changes of these reactions have also been calculated by using standard thermodynamic relations. Entropy changes of both the systems are found to be independent of percentage exchange. The enthalpy change of copper-complex is constant but that of Ni- complex decreases as the percentage exchange increases.