The adsorption capacities of five proteins and an amino acid derivative with the so-called "tentacle-type" ion exchanger LiChrospher 1000 SO3- were studied as a function of the concentration of the displacing salt NaCl in batch equilibrium experiments, thus allowing the displacement slope parameter, B, to be calculated. In general, the slopes (B) of the plots of adsorption capacity versus displacing ion concentration were negative under the experimental conditions used, consistent with the adsorption mechanism having a dominant ion-exchange contribution. However, the results for lysozyme and insulin demonstrated that their adsorption capacities increased with the concentration of displacing salt in the solution, indicative of a significant contribution of hydrophobic interaction to the binding process of these two biosolutes. The relationship between the adsorption capacity at zero concentration of displacing ion (qm,i = 0), the displacement slope parameter (B) and the experimentally derived stoichiometric displacement parameter (Zc), calculated from the ion-exchange gradient elution chromatographic results of these test solutes were compared under the same buffer, temperature and displacing salt conditions. These investigations have, in particular, confirmed that a reciprocal relationship exists between the value of the displacement slope parameter B measured in batch equilibrium experiments and the value of the parameter Zc calculated from the plot of the logarithm of the capacity factor (logk′) versus the logarithm of the reciprocal of the ionic strength at elution (log 1/C). It can thus be concluded that B is directly related to the reciprocal of the effective (or average) number of binding sites on a protein molecule involved in the interaction with the ion-exchange adsorbent.