 Myasthenia gravis is a rare neuromuscular disorder characterized by weakness and fatigability of ocular, bulbar, and extremity musculature. The specific aim of this study is to determine if oral methotrexate is an effective therapy for myasthenia gravis MG patients who are prednisone dependent. Patients will be randomized to receive either methotrexate or placebo and those who are entered onto this trial will have symptoms and signs of the disease while on prednisone therapy. The hypothesis is that adding methotrexate therapy in these patients will improve the MG manifestations so that the prednisone dose can be reduced and clinical measures of MG severity will improve. 