Cerebrospinal fluid (CSF) from 120 patients with multiple sclerosis was analyzed by polyacrylamide gel electrophoresis, as well as routine laboratory microscopy and assays of total protein and immunoglobulin G (IgG). Negative correlations were found between leucocyte counts and patient age, duration of disease and time from last clinical relapse. There was a positive correlation between the leucocyte count and amount of gammaglobulin. A correlation between gammaglobulin content and degree of disability was found. With increasing duration, the gammaglobulin concentration rose only if there was increasing disability. In terms of correlations with clinical features, differences existed depending on whether IgG was assayed immunologically or by electrophoresis and densitometry. Evidence of increased blood: CSF barrier permeability (transudation of high molecular weight proteins) was found in patients with progressive disease. The presence of oligoclonal bands was the CSF abnormality most frequently encountered.