Mucociliary transport function can be determined by ciliary motility of airway epithelial cells, the amount and physicochemical properties of airway surface fluid, and the airway integrity. Mucus glycoprotein is released from submucosal glands and goblet cells in response to a variety of stimuli and, on other hand, water is secreted by airway epithelial cells through the movement of electrolytes. Marked airway goblet cell hyperplasia has been found in patients who died of severe asthma, indicating that goblet cell hypersecretion may play a significant role in the formation of mucus plugs in the respiratory tract. Goblet cell secretion is regulated by autonomic nerves and various chemical mediators associated with asthma. Antigen challenge causes an increase in mucus discharge from goblet cells in ovalbuminsensitized animals, and this effect can be greatly inhibited by an histamine H2-receptor antagonist. Similarly, histamine released by antigen challenge stimulates airway epithelial Cl secretion and, hence, water secretion toward the airway lumen. There is ample evidence that mucociliary clearance is impaired in patients with asthma, which results in deterioration of airflow limitation. The precise mechanism for this impairment remains uncertain, but bronchospasm and the increased mucus secretion induced by peptide leukotrienes may be involved.