Blood flow regulation in the foot under a heated (43 degrees C) transcutaneous oxygen tension (tcPo2) electrode was studied in six young subjects. Blood flow under the electrode was estimated from the electrical power consumption of the thermostatistically-controlled heating element in the electrode. Changes in arterial and venous pressures, and thereby in perfusion and transmural pressure and blood flow were induced by elevation and lowering of the foot and by venous stasis. tcPo2 was significantly and positively correlated to the blood flow under the electrode, and blood flow neither showed autoregulation nor vasoconstrictor response as judged from the power consumption. In contrast the blood flow in normal unheated skin measured simultaneously by the 133-Xenon technique showed autoregulation as well as vasoconstrictor response. It is concluded that tcPo2 is a parameter determined by many variables, of which the arterial blood pressure is of particular clinical importance.