While fluid management is established in controlled hemorrhagic shock, its use in uncontrolled hemorrhagic shock is being controversially discussed, because it may worsen bleeding. In the irreversible phase of hemorrhagic shock that was unresponsive to volume replacement, airway management and catecholamines, vasopressin was beneficial due to an increase in arterial blood pressure, shift of blood away from a subdiaphragmatic bleeding site towards the heart and brain and decrease of fluid resuscitation requirements. The purpose of this multicenter, randomized, controlled, international trial is to assess the effects of vasopressin (10 IU IV) vs. saline placebo IV (up to 3 injections at least 5 min apart) in patients with prehospital traumatic hemorrhagic shock that persists despite standard shock treatment. The study will be carried out by helicopter emergency medical service teams in Austria, Germany, Czech Republic, Portugal, the Netherlands and Switzerland. Inclusion criteria are adult trauma patients with presumed traumatic hemorrhagic shock (systolic arterial blood pressure <90 mmHg) that does not respond to the first 10 min of standard shock treatment (endotracheal intubation, fluid resuscitation and use of vasopressors) after arrival of the first emergency physician at the scene. The time window for randomization will close after 30 min of shock treatment. Exclusion criteria are terminal illness, no intravenous access, age <18 years, injury >60 min before randomization, cardiac arrest before randomization, presence of a do-not-resuscitate order, untreated tension pneumothorax, untreated cardiac tamponade, or known pregnancy. Primary study end-point is the hospital admission rate, secondary end-points are hemodynamic variables, fluid resuscitation requirements and hospital discharge rate.