Using pure leukotriene D4 (LTD4) as the agonist, we determined the dissociation constants, Kb and pA2 values, for the selective leukotriene antagonist FPL 55712 on guinea pig ileum, trachea, and parenchyma. Responses of the 3 tissues to LTD4 were competitively antagonized by FPL 55712. Kb and pA2 values were similar for trachea and parenchyma. However, these values differed from those obtained in ileum. We propose the existence of multiple LTD4 receptors, with those in lung differing from LTD4 receptors in ileum.