15 patients with progressive Multiple Sclerosis (MS) were treated by an induction Cyclophosphamide (CFX) schedule followed by bimonthly boosters over one year. Of the 14 patients who completed the trial, only two displayed worsening of neurological status. Cerebrospinal fluid (CSF) total protein, IgG/Alb ratio and IgG index decreased at 6 months and were still low at the end of the treatment. Pretreatment percentages of PB CD8+ and CD4+CD45RA+ lymphocytes were lower in MS patients in comparison with healthy controls. However, no significant shifts occurred in percentage of PB CD4+, CD4+CD45RA+, CD4+CD45RA-, CD8+ lymphocytes of MS patients during immunosuppressive treatment. The lack of changes in the investigated immunological parameters contrasts with the good clinical response and the low rate of serious side effects during this treatment schedule.