Hemorrhagic shock was produced in conscious rats by bleeding the animals to a mean arterial pressure of 40 mm. Hg which was maintained for 1 1 2 hours. The animals were then treated by various means. Intravenous infusion of ATP-MgCl2 (adenosine triphosphate-magnesium chloride) before, during, or after a prolonged period of shock proved beneficial in the treatment of shock whereas ATP alone was beneficial only when given in early shock. Animals receiving ATP-MgCl2 had an 83 percent survival rate, whereas those receiving ATP alone or ADP-(adenosine diphosphate-), AMP-(adenosine monophosphate-), or adenosine-MgCl2 or Ringer's lactate had 100 percent mortality rate when treated after prolonged shock. The beneficial effect of high-energy phosphate compounds was specific to ATP-MgCl2. The effect of ATP-MgCl2 does not appear to be through vasodilatation alone since more potent vasodilating agents, such as ADP or AMP failed to produce any beneficial effect. © 1974.