Medical treatment of multiple sclerosis(MS) consists primarily of corticosteroid therapy to enhance recovery from relapse and drug interventions to help manage symptoms. However, disease-modifying drugs for the treatment of MS have been developed recent years, including interferon(IFN) beta, glatiramer acetate, and mitoxantrone. In addition to reductions in annual relapse rates and other measures of clinical disability, these drugs appear to reduce disease activity on MRI. In Japan, IFN beta-1b(Betaferon) is available as a disease-modifying drug from September 2000. This article focuses on the use of IFN beta for MS on the basis of available clinical data.