Decomposition of a palladium compound by ion irradiation has been used to catalyze electroless plating on polyimide. First, palladium-acetylacetonate or -acetate is spin-coated on a polyimide substrate. The thin resist film is then irradiated through a mask with He or Ar ions of 100 keV energy. After washing off the film parts which were not exposed to the ion beam, copper is deposited on the catalyzed polyimide substrate in an alkaline electroless plating bath. When using alkaline resistant polyimide, copper lines several microns thick can be plated. The chemical surface composition of the Pd-compounds after ion beam exposure has been investigated with ESCA. It has been found that the Pd is partially reduced. Pd-acetate is more effective to form catalytic sites than Pd-acetylacetonate.