This short monograph describes a trial of interferon beta-1b in patients with primary progressive multiple sclerosis (PPMS) or transitional MS. Designed as a randomized, placebo-controlled pilot, the trial randomly placed 73 eligible patients into two groups, placebo or interferon beta-1b 8 MIU given subcutaneously every other day for two years. Significant differences favouring interferon beta-1b in the MSFC score, T2 lesion volume and TI lesion volume at 24 months were observed. Further study of interferon beta-Ib therapy in PPMS patients in warranted.