Damage to or dysfunction of respiratory epithelial cells may contribute to the etiology of bronchial hyperreactivity in asthma and airway infection. In the vascular system, endogenous neurohumoral mediators can cause either relaxation or contraction of the smooth muscle of the blood vessel wall because they cause the release of relaxing or contracting factor(s), respectively, from the vascular endothelial cells. This brief overview summarizes data from the author's laboratory, which suggests that release of relaxing factor(s) from epithelial cells contributes to the regulation of bronchomotor tone.