Chronic obstructive airway diseases are treated by administering an osmotically active compound such as a salt, sugar, sugar alcohol, or organic osmolyte to the afflicted airway surface. The compound may be administered as a liquid or dry powder aerosol formulation. Diseases that can be treated by the method include cystic fibrosis, chronic bronchitis, and ciliary dyskinesia. The formulations of the invention can also be used in conjunction with other active agents such as bronchodilators, sodium channel blockers, antibiotics, enzymes, or purinoceptor agonists on airway surfaces.