This Phase IIB proof-of-concept study would examine the effects of an investigational product called N-acetylcysteine (NAC) on the basic processes that cause inflammation in CF lung disease. We hope to learn more about the causes of lung disease in cystic fibrosis by studying the characteristics of the inflammation in the lungs of patients who have CF.

Inclusion Criteria:

1. Male or female 7 years of age or older

2. Diagnosis of CF based upon the following criteria:

   1. One or more clinical features characteristic of CF AND (b or c)
   2. Positive sweat test > 60 mEq/L by quantitative pilocarpine iontophoresis
   3. A genotype with two identifiable mutations consistent with CF

3. Written informed consent (and assent when applicable) obtained from subject or subject's legal representative

4. Clinically stable with no evidence of acute upper or lower respiratory tract infection within 4 weeks prior to enrollment

5. Stable mild or moderately severe lung disease defined by an FEV1 > or = 40% and < or = 85% predicted for age based on the Wang (males < 18 years, females < 16 years) or Hankinson (males > or = 18 years, females > or = 16 years) standardized equations

6. Able to tolerate sputum induction with 3% hypertonic saline and to expectorate

7. Able to perform repeatable, consistent efforts in pulmonary function testing

8. Weight > or = 25 kg at time of enrollment

9. Females of child bearing potential must be willing to use birth control (IUD, oral, transdermal, or parenteral contraceptives; abstinence)

Exclusion Criteria:

1. Clinically significant liver enzymes (AST, ALT or GGT) > 2.5 times the upper limit of normal at screening

2. History of ABPA, unless have evidence of a stable IgE (< 5% increase compared to previous test) for 6 months prior to enrollment

3. Current or history of rheumatic or collagen vascular disorders

4. Use of NSAIDS other than for chronic therapy within 1 week prior to enrollment

5. Initiation of chronic therapy with ibuprofen, azithromycin, TOBI® or Aztreonam within 6 weeks prior to enrollment

6. Consumption or inhalation of antioxidants (including NAC, GSH, Immunocal, Nacystelyn, pentoxyfilline) within 6 weeks prior to enrollment

7. Use of oral or IV corticosteroids within 4 weeks prior to enrollment

8. Use of acetaminophen within 3 days prior to enrollment

9. Unable to forego during the study:

   • Vitamin E: more than 400 IU/day for subjects < or = 12 years of age and 800 IU/day for subjects > 12 years of age
   • Vitamin C: more than 0.5 gm/day
   • More than two alcoholic drinks per day

10. Known hypersensitivity to oral PharmaNAC®

11. Current cigarette consumption

12. Pregnant or breastfeeding

13. Subject unlikely to complete the study as determined by the Investigator

14. Any condition that the Investigator believes would interfere with the intent of this study or would make participation not in the best interest of the subject

15. Participation in trials for other anti-inflammatory or therapeutic investigational drugs within 6 weeks prior to enrollment