In this investigation, employing a highly sensitive microcalorimeter, we measure the influence of pH value and salt concentration on the heat of interaction between lysozyme and CS-IDA-Cu(II) gel. The direct enthalpy measurement of the interaction provides thermodynamic information regarding the binding behavior of lysozyme toward the immobilized metal ion. The binding enthalpy altered by adsorbed lysozyme at various pH values and salt concentrations are measured. The findings, along with the reported binding isotherm, are discussed herein. (C) 1997 Academic Press.