In 23 patients 18 to 73 years old transcutaneous PO2, relative local perfusion and cardiorespirogram during induction and end stage of anaesthesia were monitored. This method allows continuous sufficiently exact estimation of PaO2. The comparison between tcPO2 and corresponding blood gas analysis from arterial samples showed a good correlation of r=0.94. Thus continuous tcPO2 registration enables quick diagnosis of hypoxia and its therapy.