After trauma and hemorrhagic shock (T/HS), a variety of inflammatory mediators enter the systemic circulation through mesenteric lymph ducts, leading to acute lung injury and multiple-organ dysfunction syndrome. Recent studies have demonstrated that post-HS mesenteric lymph (PHSML) activates polymorphonuclear leukocytes (PMNs) and causes vascular endothelial cell and red blood cell dysfunction. Furthermore, PHSML contains proinflammatory mediators, such as biologically active lipids. The purpose of this study was to identify the lipid mediators in PHSML and plasma by liquid chromatography/electrospray ionization mass spectrometry and then estimate the biologic activities of the identified lipids on PMNs. PHSML was collected from male Sprague-Dawley rats undergoing trauma (laparotomy) plus HS (40 mm Hg, 30 minutes) or sham shock (SS). The lipids in PHSML and plasma were extracted using the methods of Bligh and Dyer, and liquid chromatography/electrospray ionization mass spectrometry was performed. The biologic activities (superoxide production and elastase release) of identified lipids on human PMNs were tested. Phosphatidylcholine, lysophosphatidylcholine (LPC), phosphatidylethanolamine, lysophosphatidylethanolamine (LPE), and sphingomyelin were detected in the PHSML. Furthermore, linoleoyl, arachidonoyl, and docosahexaenoyl LPCs and LPEs significantly increased in the PHSML of the T/HS group as compared with those of the T/SS group. In the plasma, arachidonoyl and docosahexaenoyl LPCs of the T/HS group also significantly increased in comparison with that of the T/SS group. Linoleoyl and arachidonoyl LPCs and LPEs showed the priming activity on N-formyl-methionyl-leucyl-phenylalanine-activated PMNs. The elastase release was also induced by linoleoyl and arachidonoyl LPCs. Mesenteric lymph after T/HS contains biologically active lipids, such as LPCs and LPEs with polyunsaturated fatty acids, which may be involved in the pathogenesis of acute lung injury/multiple-organ dysfunction syndrome. Copyright © 2012 by Lippincott Williams & Wilkins.