Parylene-N and parylene-C are polymers of interest for microelectronic and medical coating applications. Modifications for improved surface properties could make them even more useful in such applications. Parylene-N and parylene-C films were exposed to ultraviolet light in the presence of oxygen and analyzed with Rutherford backscattering spectrometry, secondary-ion mass spectroscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. This study shows that such exposure results in the formation of aldehyde and carboxylic acid groups near the surface of the films. At the maximum exposure dose, the concentration of oxygen in both parylene-N and parylene-C is about 13% at the film surface, and it decreases exponentially with increasing depth. Further modeling and optimization of this process would allow it to be used to tailor the surface concentration of oxygenated species in parylene for the optimization of adhesion and wettability or for the chemical binding of other moieties. (C) 2003 Wiley Periodicals,