Allergic pulmonary reactions in vivo lead to airway constriction and mucous secretion, whereas in vitro lung anaphylaxis lead to mediator release and increased mucous glycoprotein secretion from cultured human airways. Using quantitation of radiolabeled mucous glycoprotein from cultured airways as a model for mucous release, the effects of two leukotrienes, LTC4 and LTD4, were assessed. BOth biosynthetic and synthetic LTC4 and LTD4 produced dose-related increases in mucous production at concentrations of 1 to 1,000 units/ml (20 to 20,000 pg [LTD4] and 24 to 24,000 pg [LTC4]/ml). These enhancing actions were seen in 11 of 11 lung cultures, and were significantly prevented by the specific SRS-A antagonist FPL 55712. Therefore, LTC4 and LTD4, two major components of the allergic mediator SRS-A, are potent mucous secretagogues and may possibly contribute to the mucous secretion observed during allergic reactions in vitro and in vivo.