Many neuropeptides have recently been identified in human and animal airways. These peptides have potent effects on airway caliber, blood vessels, and secretions, raising the possibility that they may be involved in airway diseases such as asthma. Vasoactive intestinal peptide and peptide histidine methionine are potent bronchodilators and may be neurotransmitters of nonadrenergic bronchodilator nerves. In asthma, if these peptides are broken down more rapidly by enzymes from inflammatory cells, this might contribute to exaggerated bronchial responsiveness. Neuropeptides that are found in sensory nerves, such as substance P, neurokinin A, and calcitonin gene-related peptide, have inflammatory effects and might also contribute to the pathology of asthma if released from sensory nerve endings by an axon reflex. These findings may have important therapeutic implications for the future.