An imprint electroimmunofixation method (IEIF) was used to characterize antibodies to eight viral antigens (measles, mumps, rubella, herpes simplex type 1, varicella-zoster, vaccinia, cytomegalovirus, adenovirus) and four bacterial antigens (beta-hemolytic streptococcus, Hemophilus influenzae type B, Escherichia coli, enterococcus) in serum and cerebrospinal fluid (CSF) of 12 patients with multiple sclerosis (MS). Twelve patients matched for age and sex sex served as controls. Evidence for intrathecal synthesis of oligoclonal antibodies to one or more antigens was found in all 12 MS patients and in 1 of the controls. In the MS group, antibodies to viruses with neurotropic properties were more frequently associated with local synthesis than antibodies to other viruses and bacteria. The types and number of locally synthesized antibodies showed no correlation with disease duration and severity. The antibodies were not associated with oligoclonal CSF IgG and appear to account for only a minor fraction of the locally synthesized CSF IgG in MS.