Goblet cell hyperplasia (GCH) has been established as a pathologic characteristic of mild, moderate, and severe asthma. Abnormalities in goblet cell number are accompanied by changes in stored and secreted mucin (MUC). The functional consequences of these changes in MUC stores and secretion can contribute to the pathophysiologic mechanisms for multiple clinical abnormalities in patients with asthma, including sputum production, airway narrowing, exacerbations, and accelerated loss in lung function. CD4(+) T cells and their T-helper type-2 cytokine products are important mediators of GCH, and MUC5AC is the dominant MUC gene that is expressed in goblet cells. The mechanism of cytokine-induced GCH, the relationships between MUC gene up-regulation and GCH, and the role of ion channels are all currently being explored. The process of working out the molecular mechanisms of GCH and goblet cell degranulation should provide new targets for novel therapeutic interventions. Such new treatments are urgently needed, because mucus hypersecretion is an important cause of morbidity and mortality in patients with asthma, and no specific treatments are available.