Plasma exchange in chronic progressive multiple sclerosis: a long-term study. Plasma exchange (PE) was shown in a previous double-blind randomized controlled study to confer significant additional benefit at 1 year upon patients with chronic progressive multiple sclerosis (CPMS) treated with immunosuppressive drug therapy (ISDT). Efficacy over an extended term, indications for retreatment, and long-term toxicity are dealt with in this analysis of a larger number of patients. During the past 7 years, 200 patients with CPMS have been treated with PE and low-dose ISDT at this center. Improvement on the Kurtzke Disability Status Scale by one or more steps post-therapy and at 3-year follow-up is significant by comparison with pre-PE disability status. Clinical improvement was maintained in the majority of patients, reaching as far as a 6-year follow-up. Major life-threatening complications attributable to this combined therapy were not observed. 