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The complex phenomenon of surface contamination, leading to faulty contact performance of gold-plated connector-type contacts, has been investigated on the basis of data, samples, and observations originating from operating field equipment. Contaminated samples were collected, the environmental conditions under which they operated were determined, and their contact resistances and fritting voltages were measured. In addition the necessary analysis of their surfaces was carried out, using scanning electron microscopy (SEM), electron probe microanalyzer (EPMA), energy dispersive X-ray spectra (EDAX), and wavelength dispersive accessory (WDXA) techniques. In operating contacts there was a definite tendency for copper, silver, or zinc to migrate from the substrate or underplate through the continuous gold plating under the influence of operating voltages and currents. This, in turn, tended to increase both the rate and the extent of formation of contaminating corrosion products relative to those observed with contacts in nonoperating devices and those from laboratory tests that incorporated the relatively low air pollutant concentrations that were found at the indoor locations of operating equipments.