The increasingly recognized need for recompression therapy either for administering hyperbaric oxygen or for treatment of conditions responding to pressure alone, such as bends or aero-embolism requires better understanding of not only the toxic effects of oxygen but also the combined and possibly synergistic effects of O2 and hydrostatic pressure on physiological processes. Investigations are therefore proposed to study possible synergistic or compensatory effects of oxygen and hydrostatic pressure on fundamentally important biochemical and metabolic systems. The particular systems to be studied have been chosen to constitute a range of oxygen sensitivity or resistance and will be investigated under independently varied ranges of O2 and hydrostatic pressure. Catabolic systems of importance in energy metabolism (i.e., glycolytic and aerobic systems) prepared from tissues of varying O2 sensitivity (brain, lung and muscle) will be studied using existing apparatus and techniques developed by the principle investigator. In addition, other bio-chemical processes currently implicated in oxygen toxicity (e.g., lipid peroxidation, loss of pulmonary surfactant, the GABA pathway) will be investigated in a similar manner together with other naturally occurring O2-resistant systems. The strategy of investigation is thus to use systems with an O2-response which is partially understood and subject them to hydrostatic pressure. The latter becomes a tool in understanding the mechanisms of O2 toxicity while similarly the results obtained with different types of biochemical systems should indicate possible sensitivity to hydrostatic pressure per se and detect potentially synergistic and/or self cancelling effects.