The high corrosion resistance and good biocompatibility of titanium and its alloys are due to a thin passive film that consists essentially of titanium dioxide. There is increasing evidence, however, that under certain conditions extensive titanium release may occur in vivo. An ion-beam-assisted sputtering deposition technique has been used to deposit thick and dense TiO2 films on titanium and stainless steel surfaces. In this study, using the following measurements these TiO2 films have been investigated in a phosphate-buffered saline solution: (1) open-circuit potential versus time of exposure, (2) electrochemical impedance spectroscopy, (3) potentiodynamic polarization, and (4) Mott-Schottky plot. A higher electrical film resistance, lower passive current density, and lower donor density (in the order of 10(15) cm-3) have been measured for the sputter-deposited oxide film on titanium in contrast to the naturally formed passive oxide film on titanium (donor density in the order of 10(20) cm-3). The improved corrosion protection of the sputter-deposited oxide film can be explained by a low defect concentration and, consequently, by a slow mass transport process across the film. As opposed to TiO2 on titanium, a deviation from normal n-type semiconducting Mott-Schottky behavior was observed for TiO2 on stainless steel.