It has been assumed that exposure to oxygen and hyperbaric oxygen (HPO) is beneficial to hypoxic skin in part because oxygen directly penetrates the tissues. Thus, it was felt necessary to determine the extent of tissue permeability to oxygen in terms of elevation of the tissue oxygen tension (TOT). The evidence suggested that skin permeability is a function of skin thickness and oxygen pressure; 100% oxygen at ambient pressure did not elevate the TOT of the dermis. Hyperbaric oxygen was only able to elevate the TOT of the superficial dermis.