This study was terminated for administrative reasons. There were no safety concerns.

This was a multicenter, randomized, double-blind, placebo-controlled study of patients with severe, though stable, cystic fibrosis (CF) whose routine treatment included Pulmozyme. Patients were randomized to either continue Pulmozyme or have therapy withdrawn for 2 weeks (placebo group). Patients must have had stable CF symptoms without any change in therapy for 2 weeks prior to enrollment in order to participate.

Inclusion Criteria:

• Signed Informed Consent Form and, if applicable, Assent Form
• Age ≥ 14 years old at screening
• Proven diagnosis of CF
• Ability to perform acceptable and reproducible spirometry maneuvers at screening
• FVC ≤ 45% predicted for race, height, age, and sex at screening
• Chronic use of Pulmozyme for at least 3 months in the last year and daily or twice daily use during the 14 days prior to screening
• Stable regimen of chest physiotherapy (CPT) for at least 14 days prior to screening
• Ability to complete the 6-minute walk test at screening
• Ability to complete the 6-minute walk test and spirometry at Visit 2
• If on routine tobramycin solution for inhalation (i.e., TOBI®) or other cycled antibiotic therapy, intention to either start or stop therapy at the time of Visit 2 (based on routine therapy cycle; no other planned change in this antibiotic regimen for 28 days before or 28 days after Visit 2)
• Clinically stable with no change in medications during the 14 days prior to screening

Exclusion Criteria:

• Use of an investigational drug or device within 28 days prior to screening
• Previous episode of acute respiratory failure requiring assisted ventilation within 2 years prior to screening
• Previous lung transplant
• Any cardiac disease that would contraindicate performing the 6-minute walk test
• Pregnancy or nursing
• Known hypersensitivity or other contraindication to the use of Pulmozyme
• Previous completion or premature discontinuation of study drug or withdrawal from this study
• More than one prior screening failure for this study at any time or any prior screening failure for this study within the last 28 days

The Study being conducted under this Agreement is part of the Overall Study. Investigator is free to publish in reputable journals or to present at professional conferences the results of the Study, but only after the first publication or presentation that involves the Overall Study. The Sponsor may request that Confidential Information be deleted and/or the publication be postponed in order to protect the Sponsor's intellectual property rights.