Efficacy of Amiloride and Hypertonic Saline in Cystic Fibrosis

Inclusion Criteria: * Established diagnosis of CF * 2 gene mutations identified, or * Sweat chloride \> 60 mmol/L, and * 1 or more typical CF clinical features * Age \> 14 years * Able to perform spirometry and have post-bronchodilator FEV1 \> 50% of predicted at screening * Oxyhemoglobin saturation (by pulse oximetry) \> 92% on room air * Able to provide informed consent Exclusion Criteria: * Unstable lung disease: * FEV1 \> 15% below best clinical measurement within 6 months * Requirement for IV antibiotics within 4 weeks of screening * Requirement for any change in pulmonary medication within 2 weeks of screening * Evidence of reactive airways * Clinical diagnosis of asthma -\> 15% increase in FEV1 after bronchodilator at screening * Hypertonic saline use within 2 weeks of screening * Unwilling or unable to either continue or discontinue cyclical therapies (e.g. inhaled tobramycin) for the 2 weeks prior to screening and the entire study period * Pregnancy, breast-feeding, or unwillingness to use barrier contraception during the entire study period * History of allergy or intolerance to amiloride, hypertonic saline, quinine, albuterol, or related compounds * Renal insufficiency (creatinine \> 1.5 mg/dl) * Hyperkalemia (K+ \> 5.0 meq/L) * Investigational drug use within 30 days of screening * Radiation exposure within the past year that would exceed Federal Regulations by participating in the study