Polymer-metal hybrids are replacing steel structures in many applications. Combining metals and plastics is, however, complicated because they have very different physical and chemical characteristics. This study characterizes plastic-metal adhesion in insert-injection-molded hybrids. Diaminofunctional silane was used as a coupling agent between thermoplastic urethane and stainless steel. Before silane treatment, various surface treatments, including electrolytic polishing and different oxidation treatments, were applied to the steel inserts to understand better the bonding between silane and steel. The effects of the surface treatments and silane application on plastic-metal adhesion were studied by means of contact angle measurements, adhesion tests, and microscopic characterizations. Electrolytic polishing and oxidation of the steel inserts significantly improved the silane bonding to the steel insert, and consequently the plastic adhesion to steel. (C) Koninklijke Brill NV, Leiden, 2009