Transcutaneous PO2 was measured using a transcutaneous PO2 electrode heated to 45 degrees C on the forearm of 19 healthy volunteers. Cutaneous blood flow (CBF) was estimated indirectly from the heating power of the electrode (HP) and with an 8-MHz bidirectional ultrasonic probe by Doppler shift in a fingertip at 45 degrees C (DF). Blood flow was regulated by an upper arm cuff. Mean transcutaneous PO2 during air respiration was 86.0 +/- 6.2 Torr, and the correlation to arterial PO2 (Pao2) was 0.96 at normal blood flow. The arterial inflow was intermittently reduced in 10-15% stages of effective perfusion pressure (Peff). There was a hyperbolic decrease in PO2 when CBF was restricted in stages. A linear dependence between Peff, HP, and DF was found, which means that there is no autoregulation in the capillary bed at 45 degrees C. Transcutaneous PO2 can be also taken as an indication of CBF. The transcutaneous index, transcutaneous PO2/Pao2, is helpful for estimating local O2 availability.