Polyethylene has been treated in a CF4 plasma using parallel-plate electrodes at 13.56 MHz and an asymmetric configuration of electrodes both at 70 kHz (low frequency) and 13.56 MHz (r.f.). The chemical species involved in the plasmas and subsequent surface modifications were characterized. Plasma analysis by optical emission spectroscopy indicated that discharges obtained with asymmetric electrodes had a higher energy than those in the diode reactor. In the former case, 70 kHz plasmas had a higher energy than at 13.56 MHz. Analysis of the surface properties showed that r.f. and low frequency plasmas do not have the same kinetics concerning the fluorination process. Low frequency plasmas enhanced fluorination for short treatment times (t < 1 s) with an increase in the surface wettability whereas, at 13.56 MHz, relative long treatment times (t > 1 s) yielded highly fluorinated substrates (F 1 s-to-C 1 s ratio, 1.4), hence decreasing the wettabilities of the treated surfaces. For equivalent long treatment times (t > 5 s) the fluorine uptake of the surface is higher in the diode reactor than in the 70 kHz reactor with asymmetric electrodes but is less than that obtained in the case of 13.56 MHz with the same reactor. The most efficient discharge is therefore the 13.56 MHz discharge with asymmetric electrodes. Static secondary-ion mass spectrometry analysis indicated a substantial fluorination of the substrates due to the substitution of H by F. No modification of the surface roughness was observed by scanning electron microscopy analysis. Rutherford backscattering spectroscopy measurements showed that fluorine diffuses through the polymeric matrix.