To characterize the intrinsic adhesion properties of various metal-polyimide systems we have used x-ray photoelectron spectroscopy (XPS) to monitor interfacial reactions during metallization of cured polyimide at room temperature. In situ measurements were made in a UHV system when monolayers and submonolayers of Cr, Ni, Cu, or Ag film were successively deposited on a freshly cured PI substrate. Examination of the changes in various core electron spectra associated with the substrate and overlayer and their comparison with expected escape length effect indicate that while Cr and Ni react with the pendent oxygen in the substrate, Cu and Ag do not. A simple thermodynamic calculation shows that limiting values can be derived for the effective partial molar free energy of the pendent oxygen in PI, which may be used to predict whether a given metal will form chemical bonds with PI during metallization at room temperature. © 1984, American Vacuum Society. All rights reserved.