Hypertonic saline (HS) has been used since 1980 in the treatment of traumatised, hypotensive patients. Studies show more pronounced and stable increments in blood pressure and reduced mortality in various subgroups of patients treated with HS compared to isotonic fluids. When infused in the setting of hypovolaemia HS instantaneously expands plasma volume and improves central haemodynamics through increased filling pressures and direct myocardial stimulation. HS, as compared to isotonic fluids, causes precapillary vasodilation, reduction of cell oedema and decreased haematocrit and hence improves regional and capillary perfusion. Furthermore HS-infusion has been shown to attenuate reperfusion injury and restore cell function in cells damaged during hypovolaemic shock. Animal experiments as well as clinical studies on the use of HS are reviewed. A short description of the pathophysiology of acute hypovolaemic shock and exchange of fluids between body compartments is given.