The mechanism of adhesion failure of plated ABS and polypropylene (PP) plastics exposed to service conditions was determined. Adhesion failure, through the formation of blisters, proceeds by a corrosion mechanism which involves (a) the rapid lateral anodic dissolution of the thin electroless nickel layer at the plastic‐metal interface or (b) the relatively slower preferential dissolution of an electroless copper layer and the equally reactive adjacent electrodeposited copper layer. The rate of lateral development of blisters is related to the surface topography of the etched plastic substrate. The high‐density crack patterns and surface roughness of etched PP provide a greater path length for the anodic dissolution of the thin electroless nickel layer— thereby retarding the lateral undercutting more than with a plastic which has a relatively smooth etched surface (ABS). When the less reactive electroless copper is present in a copper‐nickel‐chromium system, the plastic substrate surface topography has no effect on the lateral rate of blister development. The weaker tendency toward blister formation is due to preferential corrosion of the relatively thick, two‐layered copper deposit.