The Neuroimmunology Branch (NIB) has during the last three years tested the tolerability and safety of monthly intravenously administered daclizumab (Zenapax(Registered Trademark)), a humanized monoclonal antibody against the IL-2 receptor alpha chain, in patients who receive interferon-beta, but responded incompletely to therapy with interferon-beta. Daclizumab has been well tolerated and inhibited inflammatory disease activity by almost 90%. Under an amendment of this protocol, it was demonstrated that the efficacy of daclizumab is maintained once interferon-beta therapy is discontinued.