The design, optimization, and scale-up of a chromatographic process using immobilized metal ion affinity chromatography (IMAC) demands a thorough understanding of the fundamental factors governing the various interactions between immobilized metal ions and proteins. The results obtained and reported in this study emphasize the role of ionic strength and pH in governing the extent and mechanism of these interactions using WGA-TREN-Ni(II) as the model system. The adsorption data for various ionic strength (0-3 M NaCI) and pH (5-9) conditions have been analyzed, both qualitatively, in the light of the information available for other systems, and quantitatively, using four isotherm models viz. the general affinity interaction theory/the Langmuir model, the Freundlich model, the Temkin model, and the Langmuir-Freundlich model. This analysis indicates that only the combined Langmuir-Freundlich model is able to explain the adsorption behavior under the whole range of ionic strength and pH relevant for IMAC. The other three models are applicable to some extent only for low ionic strength (less than or equal to0.5 M NaCl) values. It is envisaged that this investigation would be useful in developing an improved quantitative understanding of the role of solution environment in governing IMA interactions and in designing and/or optimizing protein separations on preparatory scale.