A platinum microelectrode (25 mu m diameter cylinder) heated by alternating current was used to study the reduction of oxygen in neutral phosphate buffer solution using cyclic voltammetry. Interference of the a.c. voltage on the electrode process was completely avoided when high frequency a.c. (100 kHz) was used. The electrode temperature was determined indirectly from the changes in open circuit potentials in a hexacyanoferrate(II)/(III) system. The influence of electrode orientation on the contribution of convection to mass transfer was shown by considering horizontally and vertically positioned electrodes. A linear relationship between the reduction currents and the oxygen concentrations was obtained. In all cases the oxygen reduction signals were improved upon heating.