AFM and zeta potential measurements were applied in order to investigate the influence of adsorption phenomena on the adhesion behavior of polymer materials. It is shown by means of zeta potential measurements that hydroxyl anions adsorb much stronger than chloride anions onto poly(etheretherketone) surfaces. The adhesion forces between the PEEK surface and the silicon nitride tip of the AFM is lower in potassium hydroxide solution than in potassium chloride solution corresponding to the different adsorption free energies of the anions. For electrolyte concentrations above 0.5 mmol/liter no adhesive contact between tip and sample can be established, We propose an explanation based on the action of competitive forces in the system PEEK-electrolyte solution-Si3N4.