The cathodic behavior of titanium was investigated in inorganic buffer solutions and in fetal bovine serum through potential sweep techniques. Under cathodic polarization, the oxygen reduction and the hydrogen evolution reactions were observed. It was found that the activity of the electrode toward the electron transfer increased with decreasing the electrode surface charge. The polarization curves recorded in serum displayed the same features as those observed in inorganic buffered solutions. However, organic molecules were likely adsorbed onto the titanium surface and the adsorption reactions were potential dependant. Additionally, it was noticed that the buffer capacity of serum could be overwhelmed by the progressive interface alkalinization during cathodic polarization. Furthermore, serum affected the corrosion current of the implant materials and the effect was pH-dependent. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 100B: 544–552, 2011.