Plasma source ion implantation (PSII), a hybrid implantation technique between ion beams and immersion plasmas has been used to modify CR39 surfaces for improved wettability providing both advancing (theta(a)) and receding (theta(r)) contact angles below 5 degrees. The modifications brought to the polymer surface structure have been characterized by X-ray photoelectron spectroscopy (XPS) and its combination with chemical derivatization (CD-XPS). Oxygen desorption has been observed in spite of the very hydrophilic surfaces. C-1s XPS peak has been displaced toward greater energies, while the opposite has been found for O-1s, both involving new components and strong modi. cations after ion implantation treatment. Strong evidences about the formation of new chemical functions, like -OOH, -COOH and C=C, have been found and have provided an explanation for the increased wettability. (C) 2008 Elsevier B. V. All rights reserved.