The effects of pulmonary denervation and rejection on contractions of bronchial smooth muscle and epithelial modulation of these contractions were studied in dogs after denervation in right lung autotransplantation (n = 6) and acute rejection after right lung allotransplantation (n = 8). Immunosuppression was withdrawn from the latter group after 5 days; rejection developed after 3 additional days. A significant (p < 0.05) increase in mean peak airway pressure occurred with rejection of allotransplanted lungs. Rings cut from third-order bronchi of transplanted and contralateral unoperated (native) lungs in each animal were suspended in organ chambers for the measurement of isometric force. In some rings, the epithelium was removed mechanically. Acetylcholine (cholinergic neurotransmitter), serotonin (platelet-product), histamine (mast cell product), and endothelin-1 (endothelium-derived contracting factor) caused concentration-dependent contractions in all rings. In bronchi from native lungs, rings with epithelium contracted less than those without epithelium. This difference was lost after autotransplantation. The smooth muscle and epithelium were affected differently by autotransplantation. Contractions of rings without epithelium decreased in response to acetylcholine and endothelin-1, whereas contractions of rings with epithelium increased in response to histamine and 5-hydroxytryptamine (p < 0.05). During acute rejection, contractions were the same as those after autotransplantation. Bronchial content of endothelin increased fourfold with rejection. Relaxations to isoproterenol and prostaglandin E2 were similar in both groups. In conclusion, denervation reduced the ability of the smooth muscle to contract. The degree of acute pulmonary rejection seen in this study did not further affect bronchial contractions. Modulation of contractions by the bronchial epithelium was lost with both denervation and rejection.