To the Editor.— The article by Heng et al 1 in the MayArchivesmakes me wonder what advantage there is to topical "hyperbaric" oxygen over simple topical ambient pressure oxygen (bag unpressurized). Henry's law states that the diffusion of a gas into a liquid (in this case, oxygen into the wound surface) is directly proportional to its partial pressure. The hyperbaric technique of Heng et al who claim that it achieves 1.04 atmospheres of oxygen partial pressure (25 to 30 mm Hg pressure above ambient) theoretically will diffuse only 4% more oxygen into a wound than topical ambient pressure oxygen (1.00 atmospheres). Actually, the determination of 1.04 atmospheres in the system of Heng et al is not entirely correct unless one assumes that the ambient barometric pressure was 760 mm Hg (one atmosphere by definition) throughout the entire trial. Sepulveda, Calif, lies at 140 m above sea level (barometric