Direct measurement of mucociliary and cough clearance (MCC/CC) has been used as a biomarker in cystic fibrosis (CF). Additional knowledge of the performance of this biomarker is needed to inform exploratory clinical trial design in support of programs to develop new inhaled therapies for CF. We hypothesize that MCC/CC measurements can be used to determine the durability of action of agents like hypertonic saline (HS) which increase epithelial lining fluid height.