There are two major mechanisms for mucus clearance in the airway, both of which are dependent upon optimal mucus viscosity and elasticity. These mechanisms are severely impaired in cystic fibrosis. The physical properties of sputum can be measured using rheological methods, enabling comparison between mucus in health and in disease. Therapies which enhance mucus clearance from the airway and decrease the volume of airway secretions are collectively called "mucoactive agents." Therapies which specifically disrupt innate mucus architecture by breaking intermolecular entanglements and bonds are called mucolytic agents. Mucolytic drugs can be considered in three general categories: classic mucolytics (n-acetylcysteine), peptide mucolytics (Pulmozyme®), and non-destructive mucolytics (hypertonic saline). Using state-of-the-art rheological methods, we can characterize the physical properties of CF mucus and measure the rheologic effects of mucoactive drugs more accurately and reproducibly than what has been previously done in the literature. In this way, we will determine which of the current mucoactive agents are most effective in normalizing sputum rheology in CF, and we will gain important insights about the limitations of current mucoactive drugs.