Prostaglandin E1 (PGE1) is a potent endogenous vasodilator agent that increases peripheral blood flow. It inhibits platelet aggregation and has many other biological effects such as bronchodilation, mediation of inflammation, and various protective functions. The protective action of PGE1 has been shown on both experimental animal models of liver injury and patients with fulminant viral hepatitis. PGE1-treated cirrhotic rats had less hepatosplenomegaly, lower serum alanine aminotransferase levels and portal pressures, and higher arterial pressure than placebo-treated cirrhotic rats. There are several mechanisms of PGE1 hepatic cytoprotection: inhibiting T-cell mediated cytotoxicity, enhancing DNA synthesis of the injured liver after partial hepatectomy by stimulating cyclic AMP production, increasing ATP level in hepatic tissue to accelerate the recovery of mitochondrial respiratory function after reperfusion, and stabilizing membrane microviscosity. PGE1 is a prostanoid. The term prostanoid collectively describes prostaglandins, prostacyclins, and thromboxanes. Prostanoids are a subclass of the lipid mediator group known as eicosanoids. They are derived from C-20 polyunsaturated fatty acids, mainly dihomo--linolenic (20:3n-6), arachidonic (20:4n-6), and eicosapentaenoic (20:5n-3) acids, through the action of cyclooxygenases-1 and -2 (COX-1 and COX-2). Prostaglandins are eicosanoids. The eicosanoids consist of the prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs), and lipoxins (LXs). The PGs and TXs are collectively identified as prostanoids. Prostaglandins were originally shown to be synthesized in the prostate gland, thromboxanes from platelets (thrombocytes), and leukotrienes from leukocytes, hence the derivation of their names. All mammalian cells except erythrocytes synthesize eicosanoids. These molecules are extremely potent and are able to cause profound physiological effects at very dilute concentrations. All eicosanoids function locally at the site of synthesis through receptor-mediated G-protein linked signalling pathways.