The aim of this investigation was to study the effect of environmental pressure and surface tension on the size of gas bubbles in tissues and on their inner pressure. Due to the action of surface tension, the pressure inside the bubbles is always greater than the surrounding pressure. This phenomenon is the more marked, the smaller are the bubbles. Therapeutic compression leads to diminution of the volume of gas bubbles and thus to a rise of that portion of their inner pressure which is due to surface tension. In small bubbles the surface tension may cause their dissolution and disappearance. It is therefore correct to implement therapeutic compression in decompression sickness as soon as possible before the fusion of a significant number of small bubbles into larger ones occurs.