We have studied the leukotriene antagonistic activity of a novel compound, SR2640 (2-[3-(2-quinolylmethoxy)phenylamino]benzoic acid), in vitro and in vivo. SR2640 inhibited LTD4- but not histamine-induced contractions of guinea-pig ileum and trachea in a concentration-dependent manner. Schild plot analysis of tracheal LTD4 antagonism yielded a pA2 value of 8.7 and a slope not different from unity. SR2640 concentration dependently inhibited the binding of 0.4 nM [3H]LTD4 to guinea-pig lung membranes with an IC50 value of 23 nM. The curve was parallel to that of unlabelled LTD4 (IC50 = 2.2 nM). SR2640 was equally effective in antagonizing LTD4 and LTE4, but was much less potent in reducing LTC4-induced ileum contractions. In vivo, SR2640 in the dose range 0.03-1.00 mg/kg shifted the dose-response curve for guinea-pig bronchoconstriction induced by intravenous LTD4 administration to the right at a rate proportional to the dose of SR2640, without reducing the maximum attainable obstruction: the slope of the Schild plot was 0.99. SR2640 (1 mg/kg) also caused a significant inhibition of antigen-induced bronchoconstriction in anaesthetized guinea-pigs pretreated with pyrilamine, indomethacin, propranolol and suxamethonium. In conclusion, SR2640 appears to be a potent and selective competitive LTD4/LTE4 antagonist, and may be useful in elucidating the role of leukotrienes in human asthma.