native oxide film on the biphasic alloy Ti6Al4V was studied with scanning electrochemical microscopy (SECM). This alloy is commonly used for biomedical applications due to its biocompatibility and mechanical properties. The heterogeneously composed, n-semiconducting oxide film is of particular interest as biological systems are in contact only with these oxides and immunological rejection mechanisms may be connected to their electrochemical properties. Auger electron spectroscopy showed that the elemental composition of the oxide films on the alpha and beta phase differ from each other. Approach curves were recorded above individual grains of the alpha phase in the feedback mode with several redox mediators. They were selected to cover a wide range of redox potentials for a better understanding of the surface kinetics of the oxide layer. The electron-transfer kinetics changed strongly depending on the redox potential of the mediator with respect to the energetic position of the bandgap of the oxide film. Predictions about the value of the flatband potential on an individual phase were derived from these experiments. Furthermore, SECM images were recorded to laterally resolve different electrochemical properties of the oxide film originating from the heterogeneous composition of the oxide on both phases. (c) 2007 The Electrochemical Society.