In this investigation, we measured the influence of pH value and salt concentration on the heat of interaction between imidazole and CS-IDA-Cu(II) gel with a highly sensitive microcalorimeter. The direct enthalpy measurement of the interaction provides thermodynamic information regarding the binding behavior of imidazole toward the immobilized metal ion. The changes in binding enthalpy with the adsorbed amount of imidazole measured at various pH values and salt concentrations are discussed and the binding isotherm is reported. The binding and thermodynamic data obtained in this study can provide information on the mechanism and process of imidazole and protein binding with immobilized metal ions. (C) 1996 Academic Press, Inc.