This prospective observational study was designed to shed light on the routine use of a hypertonic hyperoncotic solution for prehospital small-volume resuscitation in trauma patients. Effects on homeostasis and haemodynamics as well as safety were evaluated. One hundred patients with haemorrhagic shock were given hypertonic hyperoncotic solution (6% hydroxyethyl starch plus 7.5% sodium chloride) by bolus infusion (approximately 4 ml/kg bodyweight). Blood was taken before small-volume resuscitation and after the patients' arrival in the emergency room and serum electrolytes, haemoglobin, haematocrit, colloid osmotic pressure and white cell counts were determined. Haemodynamic variables were evaluated before small-volume resuscitation, just before transport and on arrival. Serum sodium and serum chloride increased at best moderately between baseline and arrival (7 and 12 mmol/l, medians; P<0.001) with peak increases of 25 mmol/l for serum sodium and 23 mmol/l for serum chloride. Serum potassium and white cell counts showed no more than minor changes. Haematocrit, haemoglobin and colloid osmotic pressure dropped (7%, 2.3 g/dl and 3.8 mmHg, respectively, medians; P<0.001). On arrival oxygen saturation and systolic and diastolic blood pressure had increased (5%, 30 and 20 mmHg, respectively), whereas heart rate had dropped by 15 b.p.m. (medians; P<0.001). Five patients developed heat sensations, restlessness, voiding urge, poor taste and vomiting, which may have been hypertonic hyperoncotic solution-related. Per-protocol bolus infusions of hypertonic hyperoncotic solution containing hydroxyethyl starch do not compromise homeostasis clinically and are rarely associated with clinically manifest side-effects. The treatment regimens used (including small-volume resuscitation) provide early and effective haemodynamic control.