This study evaluates the effect of the therapy combining GA and NAC on disease activity as reflected by MRI parameters while assessing tolerability and safety.

Inclusion Criteria:

1. Clinically Definite Multiple Sclerosis (CDMS) as defined by Poser et al (Ann Neurol 1983).
2. Subjects must have at least one T1 Gd-enhancing lesion in one of the pre-treatment MRI scans.
3. Subjects must have a relapsing-remitting disease course.
4. Subjects must have had at least one documented relapse within the last year prior to the screening visit (week -10).
5. Subjects must be relapse-free and not have taken corticosteroids (IV, IM and/or PO) within the 30 days prior to the screening visit.
6. Subjects may be male or female. Women of child- bearing potential must practice a medically acceptable method of birth control. Acceptable methods include oral contraceptive or double-barrier method (condom or IUD with spermicide).
7. Subjects must be between the ages of 18 and 50 years inclusive.
8. Subjects must be ambulatory, with a Kurtzke EDSS score of between 0 and 5.0 inclusive.
9. Subjects must be willing and able to give written informed consent prior to entering the study.

Exclusion Criteria:

1. Previous use of injected glatiramer acetate.
2. Previous use of cladribine within 2 years prior to screening visit (week -10).
3. Previous use of immunosuppressive agents in the last 6 months.
4. Use of experimental or investigational drugs, including I.V. immunoglobulin, within 6 months prior to study entry.
5. Use of interferon agents within 60 days prior to the screening visit.
6. Chronic corticosteroid (IV, IM and/or PO) treatment (more than 30 consecutive days) in the 6 months prior to study entry.
7. Chronic use of antioxidant substance(s), including NAC, (more than 30 consecutive days) within 60 days prior to the screening visit.
8. Previous total body irradiation or total lymphoid irradiation (TLI).
9. Pregnancy or breastfeeding.
10. Significant medical or psychiatric condition that affects the subject's ability to give informed consent, or to complete the study, or any condition which the investigator feels may interfere with participation in the study (e.g. alcohol or drug abuse).
11. A known history of uncontrolled asthma.
12. A known history of sensitivity to mannitol or acetylcysteine.
13. Inability to successfully undergo MRI scanning.