The method of dc surface resistance is used as a tool to measure trace amounts of Pb2+ in an aqueous ClO4 electrolyte. Long term stability is obtained with epitaxial Ag(l 11) films grown on Si(l 11). Various potential step and linear scan experiments were applied, yielding nearly the same resistance dependence on the surface coverage. The limit of detection is below 10(-6) M of Pb2+. (C) 2003 Elsevier B.V. All rights reserved.