Multiple sclerosis (MS) is an inflammatory and demyelinating disease of the central nervous system (CNS) that preferentially affects young adults. While its etiology is unknown, current concepts assume that CD4+ helper T cells with specificity for components of the myelin sheath initiate the pathogenetic process. The activation and expansion of such autoreactive T cells involves the secretion of autocrine growth factors, particularly interleukin-2 (IL-2), and the concomitant expression of its receptor, IL-2R, on the surface of T cells. Since only activated T lymphocytes can migrate through the blood brain barrier into the CNS and induce the inflammatory process, blocking the IL-2R should have an impact on disease activity in MS.