Electrochemical impedance spectroscopy (EIS) and d.c polarization resistance measurements (R-p) were used to study the corrosion resistance of surface layers produced by nitrogen ion implantation into copper substrates. Ion implantation was carried out using a Wickham ion beam generator, applying an acceleration voltage of 100 keV, a mean current of 0.40 mA and a nitrogen dosage of 4 x 10(17) ions cm(-2). Surface analyses were made by Auger electron spectroscopy (AES). Electrochemical measurements (EIS and R-p) performed in a 0.6M sodium chloride solution show nitrogen-implanted specimens have greater a.c. and d.c. apparent polarization resistance than nonimplanted specimens. The results obtained with electrochemical measurements indicate that nitrogen ion implantation in copper forms a protective surface layer which improves the corrosion resistance of the pristine material, a feature of great interest for the design of new contact materials for the electricity and electronic industries.