Abstract: An electrode (20) for electrochemical measurements in aqueous solutions at high temperatures, especially measurements in water in or from a primary or secondary circuit of a nuclear reactor in operation at a temperature of the water substantially prevailing at that time, comprises a conductor (21) of a platinum-group metal which for part of its extension is enclosed within a casing (22) making tight contact with the conductor and consisting of sintered-together particles of aluminum oxide, zirconium oxide or other electrically-insulating material which is inert to water. The conductor has one part (21a) exposed the aqueous solution and one connection part (21b) for connection to an electrical measuring member.