Abstract: A transcutaneous blood oxygen measuring device is disclosed for the noninvasive measurement of oxygen partial pressure in arterial blood which includes a cathode surrounded by an anode held together by an insulating plastic in an electrode part, a heating portion to heat the skin of a subject to which the device is applied and to receive the electrodes plus an electrolyte. The heating portion has an opening to indirectly expose the electrodes, via an electrolyte and associated membrane, to the subject's skin surface. Adjacent the working surfaces of each electrode an electrolyte is provided, retained by an oxygen permeable membrane which, in turn, is brought into contact with the subject's skin. The working face of one electrode, typically the cathode, is extended beyond the plane of the working face of the other electrode; the opening in the heater is smoothly rounded and the cathode plus tapered hole, both having approximately the same cross-sectional area, are placed in close proximity with each other.