A method and prognostic kit for assessing severity of MS in a subject suffering from MS, or for monitoring progression of MS in a subject suffering from MS, or for monitoring the effect of therapy administered to a subject suffering from MS. In both the method and prognostic kit, the level of one or more kynurenine pathway compounds in a tissue or body fluid of the subject suffering from MS are compared with a reference value for the one or more kynurenine pathway compounds.