A method for rendering a surface covered by a plastic material more hydrophilic by treatment with a gas plasma non-polymerizable gas. The method is characterized in that the intensity of the plasma is selected so that the surface becomes permanently more hydrophilic. Also disclosed is a naked plasma treated surface of plastic having an immediate water contact angle of 30, said water contact angle is changed 20 and/or less than 5% upon washing with an ethanol/water mixture (70% w/w).