133Xe washout measurements were used to determine cutaneous and subcutaneous blood flow beneath a specially designed double-thermostat tc-PO2 electrode. The skin blood flow was determined using thermal methods based on reduced heat dissipation during blood flow cessation. A total of 20 measurements were performed on two healthy volunteers, using the volar side of the right forearm as the experimental area. Cutaneous as well as subcutaneous blood flow increased with increasing electrode temperature. The cutaneous blood flow increased from 12.3 +/- 1.3 ml (100 g)-1 X min-1 (37 degrees C) to 49.1 +/- 5.4 ml (100 g)-1 X min-1 (45 degrees C) and the subcutaneous values from 20.9 +/- 0.2 ml (100 g)-1 X min-1 to 57.3 +/- 0.5 ml (100 g)-1 X min-1. Preheating of the measuring area or injection of papaverine as blood flow accelerator did not increase the maximum blood flow values. A considerable inter-individual difference between cutaneous and subcutaneous blood flow was observed, but in spite of that a good overall correlation between the 133Xe washout measurements and the two thermal flow measurements was found (r = 0.932 and 0.945, respectively). It is concluded that in some cases, but not always, measurements of tc-PO2 at electrode temperatures of 45 degrees C take place on a maximally perfused skin and that it is possible to determine skin blood flow by means of determinations of the heat dissipated from the tc-PO2 electrode to the underlying skin.