Inclusion Criteria:

• Patients must have MGFA MG grades 2, 3, or 4 generalized myasthenia gravis, according to the MGFA classification system
• Elevated acetylcholine receptor antibody (AChR-Ab) titer.
• Patient's signs and symptoms should not be better explained by another disease process.
• Prednisone dose of at least 10 mg/day (or the equivalent in alternate days) and the subject must be on a stable dose of prednisone for 30 days prior to the screening visit. Additionally, the patient must meet the steroid-dependency definition as outlined in the protocol.

Exclusion Criteria:

• A history of chronic degenerative, psychiatric, or neurologic disorder other than MG that can produce weakness or fatigue.
• Other major chronic or debilitating illnesses within six months prior to study entry.
• Female patients who are premenopausal and are: (a) pregnant on the basis of a serum pregnancy test, (b) breast-feeding, or (c) not using an effective method of double barrier (1 hormonal plus 1 barrier method or 2 simultaneous barrier methods) birth control (birth control pills, male condom, female condom, intrauterine device, Norplant, tubal ligation, or other sterilization procedures).
• Altered levels of consciousness, dementia, or abnormal mental status.
• Evidence of thymoma on chest CT or MRI. Such a finding could require immediate thymectomy and would preclude entry into the study.
• Thymectomy in the previous three months.
• Patients who have been medicated with azathioprine, cyclosporine, cyclophosphamide, mycophenolate mofetil, IVIg, or other immunosuppressive drugs within the last 60 days.
• Chest X-ray with evidence of tumor, infection, or interstitial lung disease.
• Clinical history of chronic or recurrent infections.
• Daily use of non-steroidal anti-inflammatory drugs (NSAIDs).
• History of renal or hepatic insufficiency or liver enzymes greater than the upper limit of normal.
• History of bone marrow hypoplasia, leucopenia, thrombocytopenia, significant anemia, clinical or laboratory evidence of immunodeficiency syndromes.
• Forced Vital Capacity (FVC) <50% of predicted.
• MG Grade 1 (ocular only) or 5 (crisis, requiring ventilator).
• Prior use of methotrexate for any condition.