The transcutaneous technique of measuring oxygen(tcPO2) and carbon dioxide(tcPCO2) was studied in 25 adults, without cardiopulmonary dysfunction, undergoing enflurane-nitrous oixde or pethidine-diazepam-ditrous oxide anesthesia, to determine the relationship between tcPO2, and PaO2, tcPCO2 and PaCO2. Transcutaneous measuring values were accurate clinically useful trend indicators of arterial blood gas changes under general anesthesia(tcPO2: r=0.93, tcPCO2: r=0.86). Although such a technique was less predictable of absolute arterial values in anesthetized subjets, because of many variables, it was a noninvasive, continuous method for monitoring. It is suggested that more widespread application of such monitoring awaits definitive development of a precise electrode and technique.