Bradykinin (BK) has several effects on airway function which may be relevant in obstructive airways disease. These effects are mediated via B2-receptors. BK is a potent bronchoconstrictor in animals and humans in vivo. Bradykinin contracts airway smooth muscle, is a potent bronchial vasodilator, increases microvascular leakage, stimulates epithelial cells to release bronchodilators and stimulates mucus secretion. Perhaps its most important action is the activation of sensory nerves in airways, leading to reflex bronchoconstriction, coughing and neurogenic inflammation through the release of neuropeptides from sensory nerves.