The aim of this prospective study is to evaluate prostanoid (prostacyclin and thromboxane) and lipid peroxide levels at the portal and hepatic veins, and their relation to immediate postoperative liver function. Nineteen patients with liver cirrhosis undergoing orthotopic liver transplantation were prospectively studied. Blood samples were obtained within 5 min and 1 and 2 hr after reperfusion of the new liver, through a catheter placed at the portal vein in the recipient and another at the left hepatic vein in the donor liver. Plasma prostacyclin and thromboxane were analyzed by HPLC and RIA. The formation of lipid peroxides was determined and expressed in terms of thiobarbituric acid-reacting substances. Immediate postoperative liver function was evaluated using the transaminase levels within the first 48 hr and the early postoperative graft function score, as described previously. After reperfusion, only determinations at 5 min were related with liver function. Either prostacyclin (R = -0.61, P = 0.004) levels at the hepatic vein or prostacyclin production (subtraction between hepatic and portal vein levels) (R = -0.47, P = 0.04) correlated significantly with the early postoperative graft function score. Besides, there was a significant relationship between lipid peroxide production as measured by thiobarbituric acid-reacting substances and a worse early postoperative graft function score (R = 0.61, P = .005). These results suggest that prostacyclin released after liver grafting attenuates preservation and reperfusion damage of the liver, supporting the hypothesis that there is an imbalance of prostanoids within the microvasculature in patients with a compromised postoperative liver function. Our results agree with the involvement of some degree of lipid peroxidation products in the damage of hepatocytes during anoxia and reperfusion.