We report our experience with continuous, transcutaneous monitoring of capillary oxygen and carbon dioxide tension (PtcO2PTlcCO2) during the entire length of hemodialysis treatment in 8 pediatric patients. The relative changes in PtcCh and PtcCO2 observed with this method were in accordance with those reported in the literature, obtained with frequent arterial blood sampling. There was a temporary fall of PtcCO2, averaging 26.2% after 2 h of dialysis, with a concomitant rise of PtcCO2 of 9.9%. The noninvasive, transcutaneous measurement of PtcCO2 and PtcCO2 is a reliable and valuable adjunct for the monitoring of the dialysis patient who is prone to develop hypoxemia. It is particularly useful in the very young.