This proposal requests the purchase of the Eppendorf apparatus for measuring the p02 in tissues using an automated technique based on a specially developed micro Clark electrode. We request this apparatus for several inter-related purposes. It now has become almost mandatory either to use this apparatus for the principal measurements of tissue p02 or to use it to compare measurements of p02 in tissues for both clinical and animal experiments made by other methods, including conventional microelectrodes, because the Eppendorf apparatus has rapidly become the "gold standard" for such measurements. It is especially important to relate measurements made with new technologies such as EPR oximetry techniques in order to have full credibility for the additional capabilities of the new technique; this includes considerations of the potential different domains sampled by two techniques. The highly evolved construction of the Eppendorf apparatus makes it the Clark electrode system of choice for several types of measurements including: tissues such as muscle and liver for which measurements with conventional Clark electrodes are very different because of the fragility of the electrode tips; for low p02 values such as occur in tumors and in ischemia because the usual size of other commercial electrodes consumes too much oxygen; the capability that is unique in commercial instruments: the ability to carry out a highly controlled pattern of measurements along a track, using programmed steps and internal recalibrations. The Eppendorf system is the only available commercial instrument with the requisite sensitivity, ruggedness, and availability of essential components. In spite of its relatively high price, it would be less expensive to obtain and maintain that a self-constructed system because the attainment of the capabilities to produce comparable homemade oxygen electrodes requires many years of experience and the addition of the other capabilities such as the controlled penetration of the electrode tip and the rugged construction would add significantly to that time. Development of our own equivalent "Eppendorf" would divert critical effort away from new research into attempts to reproduce established technology. Within the body the proposal we indicate specifically how the availability of the Eppendorf apparatus will greatly facilitate the progress of all four of the major users who have collaborated in this proposal. We have included sufficient additional components to make it feasible to have maximal efficiency and effectiveness with multiple users of this apparatus.