There is emerging evidence that matrix metalloproteinases (MMPs) might be involved in blood brain barrier (BBB) breakdown in multiple sclerosis. A group of natural tissue inhibitors of metalloproteinases (TIMPS) regulates proteolytic activity to prevent tissue damage. TIMP-1 and MMP-9 are known to be secreted as heterodimers and TIMP-1 preferentially functions to inhibit MMP-9 activity. In this present study, the effects of IFNbeta-1a on serum MMP-9 and TIMP-1 were evaluated longitudinally during a one-year period. The MMP-9 levels showed no significant changes while TIMP-1 levels gradually and significantly increased during 3rd and 6th months of therapy compared with pretreatment levels.