We examined the effect of removal of the epithelium on antigen-induced smooth muscle contraction and the release of mediators of inflammation from superfused, sensitized guinea-pig tracheal spirals in vitro. The epithelium was stripped from one-half of each trachea by mechanical means, and immunologic responses were evaluated by paired analysis. Removing the epithelium potentiated antigen-induced contraction, as reflected by a 5-fold leftward shift in the antigen dose-response curve, but the maximum response to antigen was not altered. This potentiation was not inhibited by pretreating the tissues with indomethacin (5 X 10(-6) M). At maximum concentrations of antigen removing the epithelium had no effect on the magnitude or kinetics of release of immunoreactive sulfidopeptide leukotrienes, prostaglandin (PG) D2, PGF2 alpha or thromboxane B2. Removing the epithelium did, however, significantly decrease the release of PGE and 6-keto-PGF1 alpha, a prostacyclin metabolite. Antigen-induced histamine release was enhanced by removing the epithelium; this effect varied inversely with antigen concentration. Selectively exposing either the luminal or serosal surface of an intact, superfused trachea to antigen resulted in the release of less than 5% of the total tissue histamine. Removing the epithelium from the intact trachea increased histamine release to approximately 25% following luminal but not serosal exposure to antigen. These studies demonstrate that the tracheal epithelium can act to inhibit antigen-induced airway contraction in vitro. This may in part reflect the role of the intact epithelium as a diffusion barrier which can limit the rate of influx of antigen molecules and thereby influence tissue mast cell activation.