Therapeutic effect of interferon-beta (IFN-beta) treatment has been associated with modulation of the balance between Th1, Th17, Th2 and regulatory T (Treg) cells, whereas the impact of disease modifying drugs on Th9-immunity in multiple sclerosis (MS) has not been studied. To investigate the short-term effects of IFN-beta treatment on cytokines in MS, we determined serum levels of IL-17, IL-23, IL-10, IL-4, IFN-gamma, IL-9 and TGF-beta in relapsing remitting MS patients before and 2 months after IFN-beta treatment by ELISA. MS patients showed increased IL-17, IL-23 and IL-4 levels and decreased IL-9 levels as compared to healthy controls. IFN-beta treatment only reduced IL-17 and IL-23 levels, whereas the levels of other cytokines remained unchanged. IFN-beta treatment appears to exert its earliest therapeutic effect on Th17-immunity. The influence of IL-9 on MS pathogenesis needs to be further studied. (C) 2012 Elsevier Ltd. All rights reserved.