Abstract: Transcutaneous and capillary PO₂ and PCO₂ were measured in 10 healthy adult volunteers during hyperventilation in atmospheric air and during CO₂ inhalation,and in 35 patients with respiratory diseases during tidal breathing.We observed close correlation between transcutaneous and blood gas measurements,both in PO₂ and PCO₂,much better in the latter.Transcutaneous PO₂ and PCO₂ were continually monitored in other 9 patients during bronchoscopy,showing no decrease in PO₂ during bronchoscopy,in all patients except one.We conclude that measurement of traanscutaneous PO₂ and PCO₂ is a reliable and useful method to monitor blood PO₂ and PCO₂.