The prevalence and titer of serum antibodies to several Epstein-Barr virus (EBV) antigens were compared among patients with multiple sclerosis, healthy siblings of multiple sclerosis patients, patients with other neurological diseases, and healthy non-blood-related subjects. An increased antibody response to EBV antigens was noted rather consistently in the sera of the multiple sclerosis group in comparison with the control group. A greater number of reduced ratios of serum: CSF IgG antibody to EBV-capsid antigen and antibody to EBV-early antigen components than to adenovirus, a referemce or control virus, were found in the multiple sclerosis group. Reduced ratios of these Ebv antibodies were detected more frequently or showed a trend in this direction in multiple sclerosis patients compared with the group with other neurological diseases. Our findings extend the result of an earlier report and strengthen the association between EBV and multiple sclerosis.