In gram-negative septicemia, endotoxin-induced free radicals probably damage the liver cells by membrane lipid peroxidation. Phosphotidylcholine hydroperoxide (PCOOH), a primary lipid peroxidation product can be applied as a parameter to measure the extent of liver damage. The protective effects of urinastatin and free radical scavengers, superoxide dismutase (SOD), and catalase against hepatic lipid peroxidation and tissue energy reserves in the liver during endotoxemia were evaluated in rats with gram-negative septicemia induced by cecal ligation and puncture (CLP). One hundred and sixty-five rats were divided into three groups. The first two groups consisted of 45 rats each. Group (1) was used for blood endotoxin level and liver function tests, group (2) for hepatic energy charge and PCOOH measurement, and group (3) (n = 75) for survival study. In each group, control animals received saline injection only. Urinastatin was injected twice intravenously through tail veins using 50,000 u/kg at 0 and 12 hr after CLP. SOD 90,000 u/kg and catalase 50,000 u/kg were given subcutaneously just before CLP and every 3 hr thereafter up to 24 hr. Liver and blood specimens were taken at time points 0, 12, and 24 hr after CLP. Increased concentration of PCOOH in liver denotes that endotoxemia can damage the liver by hepatocellular lipid peroxidation. Attenuation of lipid peroxidation, which correlated with liver enzyme leakage, was noted by finding significant decreased concentrations of PCOOH (P < 0.001), improvement in energy charge (P < 0.05), and survivability (P < 0.05) was seen in urinastatin or radical scavenger-treated groups. These results suggested that urinastatin has protective effect against free radical-induced lipid peroxidation probably by inhibiting proteases especially elastase, from polymorphonuclear leucocytes. SOD and catalase, which scavenged oxygen free radicals, also suppressed free radical-induced lipid peroxidation. Improvement in survivability was also seen in treated groups.