--Disease Characteristics-- Clinical diagnosis of demyelinating neuropathy, i.e.: Hereditary motor and sensory neuropathy type I Chronic inflammatory demyelinating polyneuropathy meeting American Academy of Neurology AIDS Task Force criteria Multifocal motor neuropathy and conduction block Clinically stable for at least 6 months prior to entry --Prior/Concurrent Therapy-- At least 6 months since change in immunosuppressive dose --Patient Characteristics-- Age: 20 to 80 Hepatic: No predisposition to hepatic disease Renal: No predisposition to renal disease Cardiovascular: No predisposition to cardiac disease Other: No other medical condition affecting neuropathy or study evaluation No predisposition to seizures