Asthma researchers have long recognized that abnormal mucus production and clearance play a role in the pathophysiology of asthma.1 Mucus plugs are known to be common in patients with severe asthma, and mucus plug scores, for which higher scores indicate more severe plugging, are directly correlated with airflow obstruction and markers of eosinophilic airway inflammation (i.e., higher scores or marker levels are associated with more severe obstruction). Other work has shown that mucus plugs were associated with distal deficits in regional ventilation as delineated by hyperpolarized gas magnetic resonance imaging.2,3.