A catheter sensor for measuring blood oxygen tension has been designed and constructed. The first year of experimentation will be devoted to examining the feasibility of making production line quantities of the R & D model which will be suitable for use in humans. Experimental methods will include simulating changes in temperature, pressure, rate of flow, pH, PCO2, and osmolality as they might occur in vivo. When the statistical analysis of the in vitro data indicates that the sensor is reliable and accurate, animal testing can begin. It is expected that at least ten months of animal experimentation will be performed during the first year.