As a metal, silver is well known for its antimicrobial effects. The development of nanocrystalline silver has allowed for the continuous release of silver optimizing antimicrobial efficacy. HBO therapy is part of the management of selected problem wounds. It is estimated that 100,000 HBO treatments are given annually to patients with wounds that may benefit from silver dressings. The purpose of this study is to investigate the safety of a nanocrystalline silver antimicrobial dressing and any change in efficacy when used in conjunction with HBO therapy. Silver readily undergoes a slow but progressive oxidation under normal atmospheric conditions. In the oxidized state, silver's antimicrobial effect can be diminished. Fortunately, the rate of oxidation is so slow that there is no substantial lose of clinical activity. In contrast to atmospheric conditions the hyperbaric chamber, with a partial pressure of oxygen of 150 mm Hg, may expose the dressing to oxygen values in excess of 1500 mm Hg. This presents a risk of increased silver oxidation and decrease of therapeutic effect. When the crystal size is less than 20 nanometers (as is the case with the nanocrystalline silver dressing studied), the surface to volume ratio is extraordinarily large, which might increase the rate of oxidation. Safety was evaluated by noting any adverse events during the HBO treatments. The antibacterial effectiveness of the nanocrystalline silver dressing was evaluated after exposer to 100% oxygen at a pressure of 2 atmospheres absolute for 90 minutes at depth (with a total exposure time of 106 minutes). Standard antimicrobial assays were performed against MRSA and P. aeruginosa. The data indicates that nanocrystalline silver is not significantly affected by simultaneous hyperbaric therapy. Also, no adverse events were noted suggesting that the nanocrystalline silver dressing contains no volatile components and is safe for use in conjunction with HBO therapy.