The effect of salt concentration on the affinity of a thermosensitive heteropolymer gel for various multiple-point adsorbing target molecules was examined. The gel has positively charged adsorber monomers which can interact electrostatically with negatively charged groups on the target molecules. Adsorption of the targets was found to depend strongly on the salt concentration. The adsorption affinity decreased by several orders of magnitude with a slight increase of the salt concentration, showing that, quite unlike the trivial Donnan potential effect, the negative ions of the salt compete with target molecules for the adsorption sites. We have found the power law relationship between the affinity for the target and the concentration of the coexistent salt for gels in the collapsed state.