Summary: Models that adequately reflect the complexity of human multiple sclerosis (MS) are needed, especially for preclinical testing of immunomodulatory drugs. Our group has created a unique experimental system in a New World outbred primate, the common marmoset Callithrix jacchus (C. jacchus). Following immunization with myelin, these monkeys develop a chronic, relapsing-remitting form of experimental allergic encephalomyelitis (EAE), which pathologically recapitulates the hallmark features of lesions of human MS. The MS-like lesion in C. jacchus results from a complex immune response against myelin antigens and requires both T cells and pathogenic antibodies. Studies of C. jacchus EAE have permitted the identification of a major target for pathogenic autoantibodies in MS, the myelin/oligodendrocyte glycoprotein. Other advantages of the model include a natural bone-marrow chimerism, which permits T-cell adoptive transfers between siblings, and the possibility of using different antigens to produce either inflammatory or demyelinating phenotypes of EAE. Despite their small size, sequential in vivo imaging and immunological studies are possible in these monkeys, and have been used to monitor efficacy in preclinical trials. Due to close phylogeny and high homology of immune and nervous system genes with humans, this model should fast-track the development of novel therapeutics for MS.