Polystyrene substrates were modified by radio-frequency plasma deposition from mixtures of various organic vapors (acetone, methane, methanol, and formic acid) and oxygen. The resulting surfaces exhibited a wide range of surface oxygen concentrations, as measured by electron spectroscopy for chemical analysis (ESCA). The surface hydroxyl, carboxyl, and carbonyl groups were derivatized with trifluoroacetic anhydride, trifluoroethanol, or hydrazine, respectively, and their concentrations subsequently determined by ESCA. The growth of bovine aortic endothelial cells was found to increase with the surface carbonyl concentration but did not appear to correlate with the hydroxyl or carboxyl concentrations.