The mechanism by which corrosion-generated hydroxide ion disrupts paint adhesion to steel has been investigated using x-ray photoelectron spectroscopy. For an epoxy ester primer applied to a bare steel substrate, the corrosion-induced adhesion loss is found to involve saponification of the resin adjacent to the primer/steel interface and cohesive failure of the primer film. Procedures for the analysis were developed in studies of surface saponification of a model polyester as well as of the epoxy ester primer. -- AATA