Magnetic resonance imaging (MRI) is being used increasingly as a measure of outcome in monitoring the efficacy of treatment for multiple sclerosis (MS). A major advantage of MRI is that it easily detects subclinical disease activity and thus serial MRI provides an objective and sensitive tool. In the treatment of acute attacks, corticosteroids are widely used to speed recovery from disability. Recently, methylprednisolone administered in megadose pulses was reported to reduce the conversion rate of patients with optic neuritis to MS. The beneficial effect of treatment was most apparent in patients with abnormal MRI scans. Among the immunosuppressive or immunomodulatory drugs that have been used to prevent progression or reduce relapses, interferon beta 1b is the first medication confirmed to reduce accumulations of MRI detected lesions. In a cyclosporin treatment trial, MRI studies failed to show a significant benefit. Other therapies that require further definitive study include intravenous cyclophosphamide and oral methotrexate or azathioprine. A multicenter double-blind clinical trial with mizoribine is in progress in Japan and the results will be known some time during the first half of 1997.