A new apparatus which can measure oxygen tension and temperature in the conjunctiva was tested and compared with measurements of transcutaneous and arterial oxygen tension in eight volunteers in connection with normal oxygen tension, hypoxia and hyperoxia. In hypoxia, the conjunctival oxygen tension was found to be better correlated to and in better agreement with arterial oxygen tension than transcutaneous oxygen tension. The advantages with conjunctival oxygen measurements are continuous measurements in easily accessible and well vascularized tissue with the same arterial supply as the brain. In contrast to transcutaneous measurement, the new method does not require warming of the tissue as the conjunctiva is oxygen permeable.