In this study we report a method to improve the adherence of hydroxyapatite ( HA) thin films, using an ion beam implantation treatment. Crystalline HA films were grown by a pulsed laser deposition technique (PLD), using an excimer KrF* laser. The films were deposited at room temperature in vacuum on Ti-5Al-2.5Fe alloy substrates previously coated with a ceramic TiN buffer layer and then annealed in ambient air at (500-600)degreesC. After deposition the films were implanted with N+ and Ar+ ions accelerated at high energy (1-1.5 MeV range) at a fixed dose of 10(16) cm(-2). The intrinsic mechanical resistance and adherence to the TiN buffer layer of the implanted HA films have been evaluated by nano-scratch tests. We used for measurements a spherical indenter with a tip radius of 5 mum. Different scratch tests have been performed on implanted and unimplanted areas of films to demonstrate the effects of N+ and Ar+ ion implantation process on the films properties. Results show an enhancement of the dynamic mechanical properties in the implanted zones and influence of the nature of the implanted species. The best results are obtained for films implanted with nitrogen. The modes of failure of the films under loading are described. (C) 2004 Kluwer Academic Publishers.