Abstract: A medical electrode unit has a dielectric body formed with a cavity therein in which are mounted a sensory electrode accessible from one side of the body, and a foam pad, having a surface adjacent an opposite side of the body. The foam pad is saturated with an electrolyte and adapted to be held on the skin of a patient by means of a flexible piece of material secured to the dielectric body surrounding the cavity and having a layer of pressure sensitive adhesive coated on a surface of the material. Once applied to the skin a fluid column of electrolyte extends from the skin to the sensing electrode. A protective cover is releasably fastened to the adhesive layer and extends over the foam pad until ready for use at which time it is peeled from the flexible piece of material. The flexible piece of material, in the form of a ring of foam is provided with a plurality of slits extending through the material from top to bottom in order to promote ventilation of the skin area covered by the electrode unit.