Dendritic cells (DCs) are key regulators of immune responses and have been associated with autoimmunity in animal models and human disease. The effects of interferon beta (IFN-beta), an immunomodulatory cytokine used in multiple sclerosis (MS) therapy, on DCs are not well understood. Monocyte-derived DCs at different stages of maturation were stimulated with IFN-beta and DC-phenotype and stimulatory function were measured. IFN-beta inhibited the development of DCs at early stages but enhanced DC maturation. Moreover, IFN-beta enhanced the capacity of DCs to stimulate autologous T-cells to secrete IL-13, IL-10 and IL-5. Thus, IFN-beta has both immunostimulatory and immunosuppressive effects on DCs depending on the stage of maturation.