Blood was applied directly to the electrode surface of a transcutaneous oxygen sensor (PtcO2) and the oxygen tension value obtained was compared to oxygen tension value from a conventional blood gas machine. Three hundred and seventeen blood samples were analyzed at four PtcO2electrode temperatures: 37, 40, 42, and 45°C. A linear regression of PO2vs. PtcO2blood drop (PbdO2) produced correlation coefficients (r) from 0.99 to 0.93 and standard errors from 3.2 to 4.7 torr at these temperatures.The mean time for stabilization was 51 sec. The PO2ranged from 4–150 torr. The authors conclude that an accurate PO2of blood can be obtained within 1 min by placing a drop of blood on the surface of a PtcO2electrode.