An apparatus, employing a fine‐wire probe, for the detection of insulating surface films on metal surfaces is described. A chemical cleaning procedure to prepare reliably clean palladium and gold surfaces is reported, and examples of the reproducibility of the method are given. Examples of the use of this apparatus include: the detection of high resistance areas on relay contacts taken from sealed relays, and a study of insulating base metal oxide impurities in commercial relay contacts. In the latter work, a sensitized paper test showed areas of iron and copper deposits on the contacts which could be correlated with areas of high resistance as indicated by the probe.