Patient with NAbs developed during IFN-β therapy do not have any longer beneficial effect of any IFN-β preparation and IFN-β has to be replaced with another therapy that may be less effective or carry along serious adverse effects. Hence, many NAb positive patients wish to continue IFN therapy, and these patients might benefit from treatment with IFN-α as both IFN-α and IFN-β are type I interferons that bind to the same interferon receptor (IFNAR). A full in vivo response to human IFN-α (Multiferon) comparable to that seen after IFN-β induction would suggest that the same therapeutic effect could be obtained with human IFN-α (Multiferon).We measure in vivo response of MxA 9-12 hours after administration of human IFN-α (Multiferon) and four other known IFN response markers measured with rt-PCR.