--Disease Characteristics-- Diagnosis of mild to moderate cystic fibrosis Small production of daily airway secretions Stable pulmonary course --Prior/Concurrent Therapy-- Radiotherapy: No radiation within 12 months to cause patient to exceed annual limits Other: No chronic medication for reactive airways disease At least 12 hours since inhaled beta-adrenergic agonists At least 24 hours since systemic theophylline --Patient Characteristics-- FEV1 greater than 50% predicted Other: Not pregnant Must perform reproducible spirometry