The authors studied immunoglobulin (Ig) G subclasses in the CSF and sera of patients with relapsing neuromyelitis optica (RNMO) and typical multiple sclerosis (MS). Although the total IgG concentrations were elevated in the CSF of patients with RNMO and MS, IgG1% and IgG1 index were significantly elevated only in patients with MS. The absence of the CSF IgG1 responses in the patients with RNMO may suggest less Th1 immunity and may also explain the rarity of oligoclonal IgG bands in patients with this disease.