Interleukin 6 (IL-6) appears to be a potential mediator of inflammation that may contribute to the pathogenesis of joint inflammation in RA. Anti-IL-6 monoclonal antibodies (Mab) may represent a new tool in RA treatment. Five patients with RA, after previous anti-CD4 therapy (B-F5) without antimouse immunization were included in our open pilot study. The anti-IL-6 Mab (B-E8, IgG1) was given intravenously (10 mg/day) for 10 consecutive days in hospital. No side effects were noted. Clinical and biological (C-reactive protein) improvement appeared during the treatment period. However improvement was transitory (mean: 2 months). Unexpectedly serum IL-6 levels increased in 4 patients with this treatment that seemed to have antiinflammatory effects. Further studies are required to evaluate the real benefit and the mode of action of this Mab.