Leukotrienes (LTs), metabolites of arachidonic acid through 5-lipoxygenase (5-LOX), have been known to play a role in leukocyte recruitment. However, the contribution of LTB4 to liver microcirculatory dysfunction during endotoxemia remains unknown. LTB4 receptor (BLT1) has been identified as a high-affinity receptor specific for LTB4. The present study was conducted to examine the roles of LTB4 and BLT1 in hepatic microcirculatory dysfunction elicited by LPS in mice. The number of leukocytes adhering to the endothelial cells of the hepatic microvessels and perfused sinusoids was determined 4 h after the administration of LPS (0.3 mg/kg, i.v.) to male C57Bl6 mice by in vivo microscopy. A 5-LOX synthase inhibitor, AA-861 (10 or 100 mg/kg, s.c.), was administered 30 min before LPS injection. BLT1 knockout mice were used to investigate whether LPS-induced hepatic microcirculatory dysfunction is mediated by BLT1 signaling. The expression of 5-LOX, intercellular adhesion molecule (ICAM) 1, and TNF-[alpha] in the liver was measured by real-time reverse-transcriptase-polymerase chain reaction. The administration of LPS caused significant accumulation of leukocyte adhesion to the hepatic microvessels and reduced sinusoidal perfusion when compared with saline-treated mice. The hepatic microcirculatory dysfunction elicited by LPS was minimized in mice pretreated with AA-861 or in BLT1 knockout mice. This was associated with the suppression of hepatic expression of 5-LOX, ICAM-1, and TNF-[alpha]. These findings suggest that the LTB4/BLT1 pathway mediates hepatic microcirculatory dysfunction by enhanced expression of ICAM-1 and TNF-[alpha] in a murine model of endotoxemia.