--Prior/Concurrent Therapy-- Endocrine therapy: Corticosteroid must be maintained at a constant dose during study Surgery: No thymectomy in the last 3 months Other: No plasmapheresis in the last 2 months --Patient Characteristics-- Age: 15 and over Weight: No greater than 80% above ideal body weight Hepatic: SGOT, SGPT, and alkaline phosphatase no greater than 1.5 times upper limit of normal (ULN) Renal: BUN no greater than ULN Creatinine no great than ULN Neurology: No history of relevant chronic degenerative, psychiatric, or neurologic disorder, other than myasthenia gravis, that can produce weakness or fatigue No altered consciousness, dementia, or abnormal mental status Pulmonary: Forced vital capacity at least 50% of predicted Not at high risk for aspiration Other: No active thyroid gland dysfunction as manifested by abnormal thyroid function tests or the need for current thyroid replacement Normal thyroid function tests required No other major relevant chronic or debilitating illnesses within 6 months of study Not pregnant or nursing Adequate contraception required of all fertile patients