|| I MEDSPECT is a medical mass spectrometer for continuous in-vivo measurement of tissue, blood and respiratory gases. Interfacing catheter for tissue in measurement has Teflon membrane. The permeability and perfusion rate for various gases through its membrane varied with temperature. The temperature coefficient of Teflon catheter in the range of 15℃-40℃ is approximately constant with -2% of correction per degree for oxygen and carbon dioxide. Linear correlation was confirmed experimentally. II The brain tissue gas tensions were measured in ten dogs with intra-venous anesthesia at normothermia and deep hypothermia using perfusion cooling, including circulatory arrest for 30 minutes at 20°C of cerebral temperature. On average, the brain tissue P(O2) was 15mmHg in normothermia when the arterial P(O2) showed 95mmHg and the brain tissue P(CO2) was 49mmHg when the arterial PC02 showed 30mmHg. The brain tissue carbon dioxide tension gradually decreased by cooling and increased during circulatory arrest for 30 minutes; from 45mmHg to 72mmHg. The brain tissue oxygen tension increased during cooling from 15mmHg to 41mmHg and decreased in the circulatory arrest; from 41mmHg to 36mmHg. III The ischemic muscle gas tension was measured in a 22-year-old man, who was suffered from thromboangiitis obliterans bilaterally, and had the popliteal autovein bypass surgery 3 months ago. Control oxygen tensions in the both anterior tibial muscles showed about the same; 35mmHg and 36mmHg respectivelly, and the P(O2) of the non-operated side showed remarkable low level of 18mmHg as compared with the side of arterial reconstruction surgery after 5-minutes ankle exercise.