We have investigated the role of B cells in myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) using B cell-deficient mice muMT) and mice bearing the X-linked immunodeficiency (xid). The mice were immunized with MOG(1-125 )in complete Freund's adjuvant but without use of pertussis toxin. B cell-deficient muMT mice on different genetic backgrounds (C57BL/10 and DBA/1 strains) developed EAE, although with a reduced clinical severity. Histological analyses revealed decreased demyelination in the central nervous system while the influx of inflammatory cells was similar or only slightly reduced as compared to B cell-sufficient control mice. Xid mice on the DBA/1 background also developed disease with a reduced disease severity. The anti-MOG antibody response in the xid mice was decreased, while the T cell response to MOG was unaffected. We thus demonstrate that B cells are not critical for the development of MOG-induced EAE but contribute to the severity. The contribution of B cells to pathogenesis appears to be mainly through demyelination rather than through inflammation.