In the Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease model for multiple sclerosis, regulatory CD8+ T cells prevent demyelinating disease and reduce in vivo interferon (IFN)-gamma production by anti-TMEV CD4+ blast cells in BALB/c mice. We describe here that regulatory CD8+ T cells reduce in vitro IFN-gamma production by lymph node cells from both TMEV and fowl gamma globulin immunized mice without affecting interleukin (IL)-4, IL-10, tumour growth factor-beta or tumour necrosis factor-alpha production.