An imprint electroimmunofixation (IEIF) technique was used to study measles, rubella, mumps and herpes simplex virus antibodies in serum and concentrated cerebrospinal fluid (CSF) from ten patients with multiple sclerosis (MS). Electrophoretically restricted virus-specific antibodies were detected in sera or CSF from nine of the ten patients. Comparison of the antibody patterns in matching serum and CSF samples indicated that electrophoretically restricted populations of antibody against one or more of the four viruses were produced locally in the central nervous system of nine patients. No association between the locally produced antibody populations the oligoclonal IgG of the CSF could be demonstrated. The virus-specific antibodies studied thus seem to constitute only a minor fraction of the total IgG of the CSF from MS patients.