Perivascular accumulation of mononuclear cells (MNCs) in the central nervous system (CNS) and high levels of myelin autoantigen-reactive T cells in blood and further enriched in cerebrospinal fluid (CSF) are characteristic for multiple sclerosis (MS) and suggest a role for immunoregulatory cytokines in MS pathogenesis. The difficulties inherent to measurements of cytokine concentrations in body fluids have been partly overcome by adopting techniques allowing cytokine determinations on cellular level. MS is associated with the parallel up-regulation of proinflammatory [interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), lymphotoxin-alpha, and interleukin (IL)-12] and immune response-down-regulating [transforming growth factor-beta (TGF-beta), IL-10] cytokines systemically. A preferential up-modulation of TNF-alpha and lymphotoxin-alpha is observed in clinical exacerbations and of TGF-beta and IL-10 in remissions. The B cell-stimulating IL-4 and IL-6 are also up-regulated in MS, as is the cytolysis-promoting perforin. Cytokine production is elevated to an even higher degree in the CSF than systemically, underlining the autonomy of the immune responses in the CSF. All cytokine abnormalities are demonstrable already in very early MS, manifested by acute unilateral optic neuritis associated with more than two MS-like lesions on brain magnetic resonance imaging and oligoclonal IgG bands in CSF. The cytokine abnormalities hitherto observed are not MS specific, because they can be found in other inflammatory CNS diseases, e.g., aseptic meningitis and even noninflammatory neurological diseases like stroke. The influence on cytokine profiles, e.g., suppressing proinflammatory cytokines and promoting TGF-beta and IL-10, could be an important way to identify new and promising treatments of MS.