In studies of the role of leukotrienes in inflammatory reactions, the induction of rat reversed passive Arthus pleurisy (a type III allergic reaction) was employed. Increases of exudate volume, vascular permeability, and migration of inflammatory cells in the pleural cavity were observed. The vascular permeability was enhanced biphasically during 0-30 min (early response) and during 3-6 h (late response) after induction of the pleurisy. The infiltration of inflammatory cells, mainly polymorphonuclear leukocytes, into the cavity increased and reached a maximum 6 h after the pleurisy was induced. Leukotriene B4 (LTB4), 5-monohydroxyeicosatetraenoic acid (5-HETE), and slow-reacting substance of anaphylaxis (SRS-A), consisting of LTC4, LTD4 and LTE4, were detected in the exudate by reversed-phase high-performance liquid chromatography during the early response. The contents of LTC4 reached a maximum 10 min after the challenge, followed by a rapid decrease within 1 h. The rise and decay of LTC4 correlated with the increase in vascular permeability during the early phase. AA-861, a 5-lipoxygenase inhibitor, given intrapleurally inhibited the increase in vascular permeability, cell migration, and generation of leukotrienes during the early phase of the pleurisy. These results indicate that products of the 5-lipoxygenase pathway, such as LTC4 and LTB4, may play an important role as chemical mediators in the inflammatory reaction.