Samples of Nitinol were oxidized using different procedures in order to improve their biocompatibility and prevent the release of Ni. The evolution of the surface oxide films was monitored using Auger electron spectroscopy (AES). The only procedure that led to the formation of nickel-free oxide films involved a pre-treatment with hydrogen plasma for 10 s followed by a treatment with a plasma composed of 90% H-2 and 10% O-2. Optical emission spectroscopy revealed an extremely high dissociation fraction for both the hydrogen and oxygen molecules at a discharge power of 600 W, where the luminous plasma was concentrated in a volume of about 0.1 dm(3). The extreme chemical reactivity of such a plasma resulted in the formation of an oxide film in about 15 s, meaning that external oxidation took place. The biocompatibility investigations, performed according to the ISO standard protocol using L929 cells, showed the absence of any cytotoxic effects that might be due to a contact between the biological materials and nickel. The investigation of nickel release of samples exposed to Hank's solution, measured by ICP-OES showed negligible Ni concentrations.