14 patients with chronic progressive multiple sclerosis, selected in a preliminary uncontrolled trial, were given a short course of intensive cyclophosphamide therapy, which was discontinued when the leukocyte count fell to 3000 cu.mm. 5 patients dropped out because of severe side effects. At 1 year follow-up were neurologically unchanged since admission to the trial; 4 remained stable at 2 years. The lack of clinical improvement, the high frequency of side effects and the proven oncogenicity of cyclophosphamide led us to discontinue the trial.