Results of measurements on glassy carbon used as physiological measuring electrodes and as stimulating electrodes are presented. The frequency dependence of the electrode impedance is shown to be comparable with that of metallic electrodes. Because of its inertness to body tissue, the glassy carbon electrode appears to have favourable properties for long-term implantation. When used with short current pulses, the glassy-carbon stimulating electrode shows a dominant ohmic polarisation similar to that of a silver anode; this holds for both the glassy-carbon anode and the cathode.