The rationale and design of a prospective randomized double blind study of 15 +/- Deoxyspergualin in the treatment of Multiple Sclerosis are presented. The study was started in autumn 1992 and will include more than 200 patients who will be randomized either to DSG low dose or DSG high dose or placebo. Average number of contrast enhancing lesions in monthly cranial MRIs during the first six months of treatment and change in EDSS at the end of the two-year study period will be the main efficacy parameters.