Among the diagnostic procedures aimed at defining the etiology and the pathogenesis of inflammatory myelopathies, the examination of the cerebrospinal fluid (CSF) plays a central role. Indeed, for several autoimmune and inflammatory syndromes and diseases involving the spinal cord, in addition to immunological screening of the blood, a detailed analysis of the CSF may allow the achievement of the diagnosis. Routine CSF analysis should include a detailed cytology, the evaluation of the blood-brain barrier dysfunction, quantitative and qualitative analysis of the intrathecal IgG synthesis (i.e. calculation of the IgG index and demonstration of oligoclonal IgG bands), and immunological and virological tests based on immunoenzymatic (ELISA, RIA) and molecular biology techniques (PCR, nested PCR). A more advanced step includes fluorescence-activated cell sorting (FACS) analysis of CSF lymphocytes, and, when possible, virological and immunological tests on cell culture supernatants.