Rat carrageenin-induced pleurisy was used as an acute exudative inflammatory model. The crude ethanol extract of the pleural fluid at 5 hr after carrageenin injection caused the very slow contraction of guinea-pig ileum, which was antagonized by FPL 55712 (1 microgram/ml). The ethanol extract was cleaned by LH-20 and was rendered for separation of LTC4 and LTD4 by reversed-phase high-performance liquid chromatography (HPLC). Two peaks which showed the same retention time on HPLC as those of LTC4 and LTD4 had the contractile activity of guinea-pig ileum and the ratios of the contractile activity to the height on HPLC agreed with those of synthetic LTC4 and LTD4. Two peaks of delta 6-trans-LTB4, 5S, 12R-(E, E, E, Z)-diHETE and 5S, 12S-(E, E, E, Z)-diHETE, were detected, but the appreciable amount of LTB4 was smaller than that of each delta 6-trans-LTB4 in the pleural fluid at 5 hr.