Hyperbaric medicine involves the use of barometric pressure great er than that at sea level for the treatment of diseases. The term makes no distinction between air, oxygen or any other gas used as a medium of compression. Hyperbaric oxygenation (HBO) refers to the use of pure oxygen for breathing in a hyperbaric chamber via a mask or similar device or breathing freely in a monoplace chamber pressurized with oxygen. HBO is an intermittent, high dose oxygen inhalation therapy. We have confined ourselves to the subject of HBO therapy and have not included oxygen therapy at normobaric pressures. With the exception of decompression sick ness we have made no attempt to cover diving medicine as many excellent treatises are available on this SUbject. Literature on HBO is extensive, and we estimate that the total number of publication on the subject of hyperbaric medicine dur ing the past 150 years exceeds 20000, nearly half published during the past 30 years. No comprehensive textbook on this topic has ever been written in English, nor is there any bibliography more up to date than 1965. The books on the subject have consisted of monographs, reports of symposia and proceedings of the various international congresses on hyperbaric medicine. No definitive work has been published in the past 10 years.