Abstract: An electrochemical electrode device comprising a tubular member having a bottom end adapted to be inserted into a liquid sample to be measured, and a top end which is closed by a cap member including electrical conductors by means of which the electrodes of the electrode device are connected to an outer cable. In order to facilitate the introduction of liquid or gel into an inner space defined within the tubular member as well as withdrawal of liquid or gel from that space, a longitudinally extending passage is formed within the cap member. This passage may be selectively opened and closed by means of a closure member which is received in a cavity extending transversely to and intersecting the longitudinal passage. The closure member is preferably in the form of a swingably mounted slide valve member or a rotatable cock member.