The interaction of chloride ions with glassy carbon electrodes is studied by means of36Cl as radiotracer. Chloride ions are bonded on the electrode in case of anodization depending on electrode potential and duration of the polarization. Strong interaction is observed at electrode potentials more positive than +1.3 V. A significant part of the chloride ions bonded at the glassy carbon can not be displaced neither by cathodic polarization nor by rinsing with water or non-labelled solutions. It is concluded that chloride ions are chemically bonded at the surface and the surface region of glassy carbon.