Twelve dogs were subjected to hemorrhagic shock by means of a modified Wiggers technique. Half were treated with prostaglandin E1, 1 microgram per kilogram per minute in 60 milliliters of saline solution, for one hour after shock, while the other half received only an equal amount of saline solution. Those dogs treated with prostaglandin E1 exhibited a significantly increased survival time and cardiac output as well as a significantly lowered total peripheral resistance when compared with those for untreated dogs. The various modes of action by which prostaglandin E1 exerts both its cardiovascular and other long term effects indicate a multisystem effect of the drug.