A chloride-selective electrode based on mercury salts on an electrically conductive epoxy support was prepared and tested. A 1+1 molar mixture of mercury(I) chloride and mercury(II) sulphide was used as the sensor. Response characteristics (linear response range, limit of detection, slope, stability and time of response, pH range and potentiometric selectivity coefficients with respect to bromide, iodide and thiocyanate) were determined. The standards of performance of the electrode were found to be better than those of a commercial electrode with the same type of sensor. Reactions taking place in the membrane are discussed.