In this study, the authors describe a new technique enabling the rapid assessment of mucociliary clearance (MCC) in rats and characterize this aspect of innate host defense in 2 animal models of bronchitis. Following instillation into the airways, fluorescent microspheres were rapidly cleared over 24 hours, with 60% to 80% of clearance occurring within 4 hours. On a background of airway neutrophilia and mucus hypersecretion, induced by either lipopolysaccharide or cigarette smoke, MCC was significantly enhanced. This reserve capacity in the MCC system will need to become overwhelmed in order to model the clinically observed impairment of lung mucus clearance in an animal system.