The association of human parvovirus B19 (PVB19) infection with the development of several systemic autoimmune diseases has been confirmed in other studies. To determine if there is any association of PVB19 infection with multiple sclerosis (MS), we studied the prevalence of serum anti-PVB19 IgG and IgM by an enzyme-linked immunosorbent assay and PVB19-specific DNA in the cerebrospinal fluid (CSF) by the polymerase chain reaction method in a total of 46 patients during exacerbation or remission of MS. Anti-PVB19 IgG was detected in 65.8% of the patients' sera. The percentage was significantly higher than that in age-matched healthy control subjects (40%; p = 0.019), but was not higher in patients with other neurological diseases (50%; p = 0.16). There was no correlation between serum anti-PVB19 IgG status and antinuclear antibodies or oligoclonal IgG bands in CSF. Serum anti-PVB19 IgM and PVB19 DNA in CSF were consistently negative in the patients during exacerbation of MS. Although MS patients may be commonly infected with PVB19, our results suggest that there is no active PVB19 infection during exacerbation of MS.