--Disease Characteristics-- Cystic fibrosis (CF), i.e.: Sweat chloride greater than 60 mEq/L Clinical manifestations of CF Homozygous delta F508 mutation preferred Compound heterozygotes for F508 mutation with pancreatic insufficiency eligible FEV1 greater than 40% of predicted PO2 at least 60 mm Hg on room air No acute or recurrent sinusitis No obstructive nasal polyposis No pneumothorax or hemoptysis, e.g., more than 250 mL blood within 24-hour period, within past year No unstable lung disease with worsening pulmonary symptoms, arterial blood gas, or pulmonary function tests within 2 weeks prior to entry No pulmonary exacerbation within 4 weeks prior to entry --Prior/Concurrent Therapy-- At least 2 months since participation in any other clinical study At least 2 months since DNase At least 4 months since corticosteroids --Patient Characteristics-- Cardiac: No severe cardiac disease Other: No other severe organ system disease, e.g., juvenile-type diabetes mellitus No pregnant women