Tannin, isolated from cotton bracts, inhibits chloride (Cl) and water secretion across the airway epithelium. Since intracellular Ca and CAMP levels regulate Cl secretion in airway epithelial cells, we examined the effect of cotton bracts tannin on the rise in intracellular Ca in response to epinephrine and bradykinin stimulation and its relationship to intracellular levels of CAMP in bovine trachea epithelial cells using Indo-1 fluorescent techniques for intracellular Ca and a radioimmunoassay kit for CAMP. Tannin had no effect on intracellular Ca or CAMP levels in response to bradykinin. In contrast, tannin inhibited the epinephrine-induced rise in both intracellular Ca and CAMP in a dose dependent fashion. These data suggest that tannin inhibits Cl secretion by affecting intracellular Ca and CAMP pathways, but not prostaglandin pathways.