The fact that as many as 60 new hyperbaric oxygen chambers are being established each year in the United States indicates the extent of interest in this relatively new therapy. In 1983 the Hyperbaric Medicine Committee of the Undersea Medical Society revised its classification of conditions being treated by hyperbaric oxygen (HBO), dividing them into two categories: category 1, conditions for which HBO treatment is known to be effective and is third-party reimbursable, and category 2, conditions for which such treatment is unproved experimentally or clinically and is not reimbursable. In the future many of the conditions in category 2 may be reclassified as category 1, which would allow HBO treatment to be third-party reimbursable.