The effect of the sulfate-reducing bacteria (SRB, Desulfovibrio desulfuricans) on the surface properties and corrosion resistance of an electropolished NiTi alloy was assessed. NiTi samples were exposed to abiotic and biotic media (Postgate medium + artificial saliva) for different exposure periods (24, 168 and 720 h). Electrochemical impedance spectroscopy (EIS) measurements were carried out in physiological Ringer's solution to assess the effect of biofilms on the electrochemical properties of the NiTi alloy. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to analyze the properties and chemical compositions of the surface that was modified with biofilm. Evident influence of SRB on the surface of the NiTi alloy was observed, and the most intense effect was observed after 168 h of bioexposure. Biofilm-covered NiTi alloy was characterized by reduced resistance (R-i) and higher capacitance (C-i) in the barrier region of the oxide. However, some restoration of the protective properties of the passive film was observed in samples that had been exposed to bacteria for 720 h. XPS studies showed that no significant changes from the surface chemistry of the abiotic NiTi samples were induced by biofilm formation. (C) 2017 Elsevier Ltd. All rights reserved.