Arterial air embolism is rarely seen except during diving operations, submarine escape training or during explosive decompression. In the present studies it was produced by decompression of tracheotomized rabbits. The animals were taken to a simulated depth of 100 ft. of water in a pressure chamber, and then during decompression, the trachea was closed at a 'depth of 60 ft.' until the surface was reached. Under these conditions the main injuries observed in a series of 10 experimental animals were, air embolism, pneumothorax and interstitial emphysema. In those cases where pneumothorax was present, the quantity of air in the blood vessels was small or absent altogether. Air appeared in the circulation only after the intra-tracheal pressure was allowed to return to atmospheric. Manual squeezing of the chest or applying an abdominal binder prior to clamping the trachea were both found to be effective in preventing these injuries in a further series of 10 rabbits. Squeezing the chest reduces the volume of air in the lungs nearly to residual. The binder not only reduces the initial lung volume by raising the diaphragm, but also provides support to the lungs during decompression. In a few human trials, subjects ascending from a depth of 100 ft. found the ascent to be more comfortable when wearing an abdominal binder than without one.