Multiple sclerosis (MS), an autoimmune disease of the central nervous system (CNS) characterized by primary demyelination, is believed to result from an autoimmune attack against myelin components. In view of their ability to induce experimental autoimmune encephalomyelitis (EAE), an animal model for MS, the quantitatively major myelin proteins — myelin basic protein (MBP) and proteolipid protein (PLP) — have been extensively studied as the relevant primary antigens in MS, and therapeutic approaches have been targeted to counteract autoimmune reactivity to MBP and PLP. Accordingly, copolymer 1, a random synthetic amino acid copolymer cross-reactive with MBP and highly protective against the induction of EAE with MBP or PLP, is now being extensively tested in clinical studies as a therapeutic agent for MS. However, increasing evidence suggests that autoimmune reactivity against other CNS-specific myelin proteins could also be involved in the pathogenesis of MS. In this context, we have demonstrated that peripheral blood lymphocytes from patients with MS respond predominantly to myelin oligodendrocyte glycoprotein (MOG) rather than to MBP or PLP, suggesting an important role for cell reactivity against MOG in the pathogenesis of MS. We have demonstrated that T-cell reactivity to MOG can also be pathogenic by inducing neurological disease in H-2^u and H-2^b mice with the same peptide of MOG, pMOG 35–55. Most interestingly, the expression of the disease differed with the different MHC backgrounds. Induction of a differentially expressed disease in different strains of mice with the same myelin antigen makes this new model particularly relevant to MS, where different expression of the disease is seen in different patients. Therefore, notwithstanding the importance of the autoimmune reactivity to MBP and PLP in MS, the potentially pathogenic autoimmune reactivity to MOG must now also be taken into consideration in therapeutic approaches to MS. In this context, we have investigated the possible effect of copolymer 1 treatment on autoimmune reactivity to MOG and on the development of EAE induced by MOG. Copolymer 1 was found to inhibit the binding of MOG peptides to MHC molecules, as well as the proliferation of MOG-reactive T cells, in a dose-dependent manner. In parallel, injection of copolymer 1 concomitantly with the encephalitogenic MOG peptide exerted a strong protective effect against the development of EAE. These preliminary data on the effect of copolymer 1 on the autoimmune response to MOG in mice indicate that copolymer 1 may also be effective in cases of MS where the autoimmune response to MOG prevails, and should therefore be further investigated in this context.