The role of various chemical mediators in the development of complications after major surgery was investigated. Phospholipase A2 activity (PLA2), and the levels of pancreatic secretory trypsin inhibitor (PSTI), polymorphonuclear leukocyte elastase (PMNE), thromboxane B2 (TxB2), 6-keto-PGF1 alpha (6-KF), leukotriene (LT) B4, C4, D4, interleukin-beta (IL-1 beta), tumor necrosis factor (TNF), and endotoxin (Et) in the serum were measured in 134 surgical patients of whom 36 developed postoperative complications. PLA2, arterial TxB2 and 6-KF showed significant changes in the patients with post-operative complications, associated with elevated Et levels. The majority of these patients had a significantly higher ratio of TxB2/6-KF. These results suggest TxB2 and 6-KF, and the TxB2/6-KF ratio are useful indices of outcome in critically ill patients with hepatic failure. Our findings revealed marked production of prostanoids in sepsis and indicate a severity of the complication in balance of the thromboxane/prostacyclin axis. It was also suggested that the opsonin and eicosanoid levels are closely related to the serum endotoxin level. LTB4, C4 and D4 were increased in the patients with postoperative sepsis or DIC, especially at the initial onsets. The increased levels of IL-1 beta or TNF were observed in some patients with postoperative complications, especially those with severe postoperative complications.