Antibody titers to varicella-zoster (V-Z), herpes simplex (HSV) and vaccinia viruses were determined in sera collected in Buffalo, NY, from patients with multiple sclerosis (MS), patients with other diseases, and normal individuals. The mixed agglutination test employing cell cultures infected with one of the above viruses as a source of antigen was used to determine antibody titers. The geometric mean titer (GMT) for V-Z in 59 MS cases was significantly higher than that observed in patients with other diseases and in normal individuals. The GMT for vaccinia was also higher in MS patients but the difference was not as great as for V-Z. No difference was observed in the titer of antibodies for HSV. Similar results were obtained for 51 MS patients compared to healthy controls matched for sex and age. Higher antibody titers for V-Z and HSV were observed in cerebrospinal fluids from MS cases than in those from non-MS CNS patients in Baltimore, MD. Antibodies to V-Z, HSV and vaccinia were detected in washing fluids from brain homogenates of MS cases.