Abstract: A dialysis electrode device comprises a shank of needle-like proportions and formed from a hollow dialysis fiber membrane. The shank is closed at its distal end by a sealing plug and, at its proximal end, it is sealed to and in communication with an auxiliary chamber defined by a tubular body part. Electrolyte is supplied to the chamber in the shank through an inlet conduit and is removed via an outlet conduit connected to the auxiliary chamber. The device also includes a dialysis or first working electrode, which is insulated save for a length thereof disposed within the hollow shank, a counter electrode and a reference electrode mounted within the auxiliary chamber. It may be used in clinical medicine and the food, pharmaceutical and other industries where it is desirable to analyze or monitor the presence of chemical substances.