An improved cell compatibility of polymers is determined by interactions with the cell surface, which are influenced by the chemical surface properties of the polymers. Of special interest are methods to change the surface properties by generating new functional groups for a better cell adhesion without affecting the bulk properties of the polymer. The study describes the surface modifications of a new flexible copolymer comprising polyvinylchloride by either wet chemical treatment or plasma treatment. In the first case the immobilization of different diols to the activated surface changes the hydrophilicity of the surface. Furthermore, for the first time the surface of the copolymer is modified by S02-plasma treatment to generate oxidized sulfur spezies at the surface. All modifications are characterized by X-ray-photoelectronspectroscopy (XPS), ATR-FTIR-spectroscopy and the contact angle. The correlation between the chemical surface properties and the fibronectin adhesion indicates the surface/biological system interactions. The S02-plasma treated surface shows the highest value of fibronectin adsorption compared to the other surface modifications. This correlates to the results of human endothelial cell culture experiments. On the SO2-plasma modified surface of the copolymer the cell proliferation is better than on surfaces modified by immobilization of different diols.