Eosinophils generate and release leukotrienes C4 and B4 (LTC4, LTB4) and platelet activating factor (PAF), all of which have the capacity to cause inflammation and tissue injury in the airways. This study has examined the effects of a new 5-lipoxygenase inhibitor, 6-hydroxy-2-(4-sulfamoylbenzylamino)-4,5,7-trimethylbenzothiazo le hydrochloride (CAS 120164-49-0, E6080) on the release of LTC4, LTB4 and PAF by human eosinophils, Eosinophils stimulated by 1 mumol/l calcium ionophore A23187 for 15 min released 37.5 +/- 2.2 ng, 2.3 +/- 0.3 ng and 4.0 +/- 0.3 pmol per 10(6) cells of immunoreactive LTC4, LTB4 and PAF, respectively (mean +/- SEM, n = 4). LTC4 and LTB4 releases were inhibited dose-dependently by the addition of E6080 to the cell suspension. The IC50 values were 0.26 mumol/l for LTC4 and 0.23 mumol/l for LTB4. PAF release was not inhibited. These results suggest that E6080 is a potent inhibitor of LTC4 and LTB4 release from eosinophils and may provide a protective effect against bronchoconstriction during late-phase asthmatic responses.