Total internal reflection microscopy (TIRM) was applied to measure the interaction potential between charge-stabilized polystyrene latex spheres and a glass wall in dependence on the concentration of additional poly(ethylene oxide). The influence of the polymer can be described by steric repulsion between polymer layers, which are physically adsorbed onto the surfaces of the polystyrene sphere and the glass wall. The expected attractive contribution to the potential due to polymer depletion was not observed. An increase of the polymer bulk concentration is shown to strengthen the steric repulsion. At the highest polymer concentrations studied, it is possible to accurately describe the experimental data for the steric contribution to the total interaction potential with the Alexander-de Gennes model for brush repulsion.