['The aim of this study was to investigate whether leukotrienes synthesized by 5-lipoxygenase (5-LO) and acting via leukotriene (LT) receptors contribute to 5-hydroxytryptamine (5-HT)-induced knee joint plasma extravasation (PE).', 'Knee joints of rats under anesthesia were perfused with 5-HT and synovial vascular Evans Blue dye leakage was measured spectrophotometrically. A series of 5-LO inhibitors and LT receptor antagonists were investigated for their ability to inhibit 5-HT-induced synovial PE.', 'Inhibitors of 5-LO (NDGA and REV 5901) significantly attenuated 5-HT-induced plasma extravasation. MK 571, LY 171883, BAY u9773 (CysLT receptor antagonists) and REV 5901 (a CysLT receptor antagonist and a 5-LO inhibitor) were equally effective in inhibiting 5-HT-induced PE, indicating that leukotrienes mediate 5-HT-induced PE via CysLT receptors. In contrast, antagonists selective for LTB(4) receptors (BLT(1) and BLT(2) receptors) failed to reduce 5-HT-induced PE.'] Do leukotrienes mediate 5-hydroxytryptamine-induced plasma extravasation in the rat knee joint via CysLT-type receptors?