The deposition of adatoms onto the surface of a thin metal film can increase its lateral dc resistance. The magnitude of the increase is related to the surface coverage. We have utilized this phenomenon for the determination of heavy metal concentrations in aqueous solution, Using thin gold films as working electrodes ina three electrode arrangement, we deposited cadmium, lead, nickel, thallium and zinc ions as well as Cd-EDTA complexes and measured the corresponding resistance changes. Different species could be distinguished from each other. For cadmium ions a linear relationship between the induced resistance change and the cadmium concentration has been achieved over a concentration range between 4 ng/g and 1 mu g/g.