Numerous experimental studies on the effects of hypertonic saline in haemorrhagic shock have been published and controlled clinical studies are now beginning to be reported. Animals suffering from an otherwise lethal haemorrhagic shock survived when given hypertonic sodium chloride solution (7.5%, 2,400 mosmol.1-1). In most studies, this solution was more efficient than isotonic fluids in treating controlled haemorrhage. Although the mechanisms involved are not yet fully understood, they certainly include the following: 1) plasma volume expansion due to osmotic fluid shifts into the vascular compartment from intra- and extra-cellular fluid reservoirs, as hypertonic saline induces hypernatraemia and hyperosmolarity, both effects linked to the sodium load; 2) non specific precapillary vasodilation of renal, coronary and splanchnic vessels; 3) arterial and venous vasoconstriction in muscle and skin, due to a vagal reflex set off by the lung osmoreceptors, the efferent pathway of which is likely to be the sympathetic nervous system; 4) increased myocardial contractility. Hypertonic saline also decreases intracranial pressure, and improves lung function during resuscitation of haemorrhagic shock. However, hypertonic saline should not yet be used routinely in man, except in controlled clinical studies. Indeed, there are as yet not enough data concerning humans. Moreover, during uncontrolled haemorrhage, hypertonic saline increased blood pressure, and therefore bleeding, thus reducing survival rates. Further clinical studies are required before hypertonic saline could be safely recommended for treatment of haemorrhagic shock.