The electrochemical corrosion behaviors of Ti-6Al-4V implant alloy were studied in three biological fluid solutions, i.e. urine, serum and joint fluid. For comparison, the corrosion characteristics of Ti-6Al-4V implant alloys were also investigated in phosphate buffered saline (PBS) solutions at different pH values and temperatures. The electrochemical corrosion properties of Ti-6Al-4V alloys were investigated by electrochemical techniques, such as cyclic voltammetry, potentiodynamic method, and ac impedance spectroscopy. The corrosion resistance of Ti-6Al-4V implant alloys in different biological solutions was evaluated in terms of corrosion potential (E-corr), corrosion current density (i(corr)) and polarization resistance (R-p). The corrosion kinetic parameters were calculated from both the Tafel extrapolation analysis and ac impedance analysis. It was observed that the corrosion current densities of Ti-6Al-4V implant alloy in PBS solutions of different pH values were about the same order of magnitude, which was at a level of 1-2 muA cm(-2) at 37 degreesC. In contrast, the corrosion current densities in biological fluids were lower at an order of 0.1-0.3 muA cm(-2) at 37 degreesC. The ac circuit elements for corrosion interface of Ti-6Al-4V alloy in various solutions were reported based on the Randle equivalent circuit model. It was found that the Ti-6Al-4V implant alloy in three biological body fluid solutions showed a characteristic of one capacitive behavior. The experimental results obtained from different electrochemical techniques were compared and discussed. (C) 2004 Elsevier B.V. All rights reserved.