Changes in work function have been measured with a Kelvin probe for the initial stages of epitaxial growth of (111) Cu on (111) Pd and (111) Pd on (111) Cu and for CO adsorption on selected bilayers at room temperature. The results of this study show that, at low metal coverages, the overlayers have properties which differ significantly from those of bulk crystals. One of the most interesting observations was that a quarter monolayer of Cu on Pd (111) increases the saturation work function change upon CO adsorption by more than a factor of three as compared to a thick Pd (111) film