Low-pressure microwave plasma has been used to incorporate new functionalities onto the surface of cyclic olefin copolymers (COC). The main goal of the plasma treatment was to hydrophilize the COC's surface in order to enhance its adhesion to metals. The effect of two plasma parameters (treatment time and type of plasma gas) on the adhesion properties has been investigated. In order to investigate the opportunity for optimization of the adhesive strength in the COC–metal composite, an adhesion-promoting layer of acrylic acid (AA), or inorganic SiO2, has been deposited. Copyright © 2004 John Wiley & Sons, Ltd.