1. A phenomenon is described whereby microbubbles of 150–250 μm diameter have been observed to disintegrate upon collision in human plasma and surfactant solutions, into many smaller bubbles of diameter 35–45 μm.
2. The thermodynamic aspects are discussed together with the physiological implications in the occlusion of vessels, enhanced haemolytic effects of air and the supersaturation of blood.
3. Air is found to dissolve much more rapidly in the form of the ultramicrobubbles resulting from collision, their ‘life’ now becoming of an order of magnitude similar to the blood circulation time in man.
4. The possible protective role of this phenomenon in preventing vascular occlusion by air embolism is discussed.