Low doses of Escherichia coli hemolysin cause thromboxane-mediated hypertension and vascular leakage in blood-free perfused rabbit lungs (W. Seeger, H. Walter, N. Suttorp, M. Muhly, and S. Bhakdi, J. Clin. Invest. 84:220-227, 1989). The recirculating buffer medium and bronchoalveolar lavage fluid from lungs exposed to hemolysin (2.5 hemolytic units per ml) in the presence of cyclooxygenase inhibitor were analyzed for leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) by reverse-phase and straight-phase high-pressure liquid chromatographic techniques combined with UV spectrum analysis and post-high-pressure liquid chromatography radioimmunoassay. A rapid release of large amounts of cysteinyl-LTs and leukotriene B4 (LTB4) into the intravascular space was noted (total sum, approximately 4 to 5 micrograms). Similar quantities have hitherto been elicited only by high concentrations of the artificial calcium ionophore A 23187. Moreover, a marked liberation of 5-HETE and 12-hydroxyheptadecatrienoic acid into the buffer medium occurred, whereas LTB4 represented the predominant compound in the lavage fluid. The hemolysin-induced burst of LT and HETE generation preceded the onset of vascular leakage. The outstanding capacity of E. coli hemolysin to produce the liberation of potent lipid mediators is probably relevant to the pathways of vascular injury and amplification of inflammatory events during severe infection with hemolytic E. coli strains.