Abstract: The invention is generally directed to methods of promoting normal respiratory tract airflow in subjects with restricted airflow and ciliary clearance caused by the presence of pathological airway contents, and particularly mucoid contents. Actin-binding proteins are administered into the respiratory tract of a subject with a pathological respiratory condition involving the presence of such contents. The actin-binding protein binds to actin polymers in the contents and decreases the viscosity. The actin binding proteins also prevent actin from binding to exogenous or endogenous DNase, thus increasing the degradation of DNA polymers in the contents.