T-cell clones derived from the CSF (cerebrospinal fluid) of MS (multiple sclerosis) patients have been analysed for the production of interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), interleukin-2 (IL-2) and interleukin-4 (IL-4). Each CSF-T clone (both CD4+ and CD8+) produced substantial amounts of IFN-gamma and especially TNF-alpha compared with autologous peripheral T clones and liver-infiltrating T clones from patients with chronic active hepatitis. The large quantities of TNF produced by CSF-T cell clones suggest an important role for this cytokine in MS immunopathogenesis.