The clinical diagnosis of definite multiple sclerosis is supported by abnormalities in the cerebrospinal fluid: variable mild pleocytosis and elevation of total protein, moderately elevated total IgG in most patients, and the almost invariable presence of discrete immunoglobulins after electrophoresis, the oligoclonal bands. The oligoclonal bands are non-specific, and are seen in most diseases of the nervous system, but their temporal uniformity in each patient with multiple sclerosis is characteristic. Prognostically, patients with a single episode of optic neuritis or paraesthesia who have oligoclonal bands are more likely to develop multiple sclerosis than if the spinal fluid were normal. In the Guillain-Barré syndrome, the spinal fluid total protein is transiently elevated, with no pleocytosis. Oligoclonal bands are usually found in the acute phase and only persist in those patients with chronic or relapsing polyneuropathy.