Remote argon plasma (RP) and ozone in the presence of ultraviolet light (UV-O-3) were used to render polystyrene (PS) surfaces hydrophilic in a controlled manner for eventual application in cell-surface interaction studies. X-ray photoelectron spectroscopy (XPS) was used to characterize both methods of modification. The degree of modification on PS was measured by an increase in surface oxygen and concomitant change in C Is binding energies as a function of time. Both remote plasma and UV-O-3 are shown to be partially surface destructive, producing polymer fragments which are easily washed away to leave stable modified surfaces of oxidized polymer comprising of distributions of C-O, C=O and O-C=O type groups. Of the two methods, UV-O-3 is shown to be more versatile and conducive to preparing PS surfaces with controllably varying degrees of modification. UV-O-3 modified polystyrene is shown to be stable in air for at least eight months. Contact angle methods were used in correlation with XPS in characterizing UV-O-3 modified surfaces. It is shown that changes in surface tension and total surface oxygen content were related, however, not directly connected.