The pzc of an Ag monolayer on Pt(l It) has been determined according to the Gouy Chapman theory by recording the capacitance-potential curves. A value of -0.48 V versus SCE was found which is 0.24 V higher than that of Ag(111). This difference is close to that expected from the difference in work functions of Ag(111) and a monolayer of Ag on Pt(111) (0.26 eV). The pzc of bulk Ag deposits is identical to that of Ag(111), confirming that Ag deposition is epitaxial.