The corrosion resistance of stainless steel is mainly caused by heterogeneities. Inclusions especially play a key role as potential initiation sites. Since most of the electrochemical techniques provide only average data integrating over a relatively large surface area (square millimeters to square centimeters) they are inadequate for studying localized corrosion processes. Use of in-situ scanning probe microscopy (SPM, e.g., scanning tunneling micrsocopy (STM), atomic force microscopy (AFM)) and tip-sample distance modulation spectroscopy in conjunction with microelectrochemical techniques with a current detection limit of ≤10 fA enables investigations in the nano-and micrometer range.