Using potentiodynamic polarization and electrochemical impedance techniques, the electrochemical behavior of carbon-fiber/polyetheretherketone (C/PEEK) composite material was studied primarily in lactated Ringer's solution with and without a stable, fast reacting redox couple (0.01M K4[Fe(CN)6] + 0.01M K3[Fe(CN)6]), at 37°C. For comparison, the spontaneous passivation of stainless steel 316L, Co-Cr-Mo alloy, and Ti-6Al-4V was also investigated in these electrolytes. It was found that the rate of total electrochemical interaction (corrosion + electron exchange) between a spontaneously passivated metal and the environment can be considerably smaller than the rate of simple electron exchange between the carbon-fiber composite and the environment. Considering the excellent biocompatibility of carbon, this finding seems to indicate the important role of protective passive films on metals, rather than the clinical significance of higher electron exchange rates in general. When the protective passive layer on the metals is damaged or removed mechanically, the undesirable effect of substantially increased corrosion rates can be observed, particularly in environments with low redox activity. While galvanic corrosion may also occur between the mechanically depassivated and the passive sites of implant metal surfaces, more considerable galvanic corrosion can be expected if the metal undergoing fretting wear is in contact with a carbon-fiber composite, depending on the anodic/cathodic surface area ratio and on the redox properties of the environment. Additionally, the repassivation of the damaged metal surface may not take place effectively. Being the most susceptible to localized corrosion, stainless steel 316L, even in the passivated condition, may show accelrated pitting corrosion if coupled with carbon-fiber composites.