The standard initial therapy for acute graft-versus-host disease (GVHD) is corticosteroids. Daclizumab is a humanized monoclonal antibody against the interleukin 2 (IL-2) receptor expressed on activated T lymphocytes. Because of daclizumab's favorable toxicity profile and response rate in steroid-resistant GVHD, a multicenter, double-blinded, randomized study of corticosteroids with or without daclizumab for initial treatment of acute GVHD was conducted. A total of 102 evaluable subjects of the targeted 166 were enrolled at 5 participating sites. Methylprednisolone at a dose of 2 mg/kg or daily equivalent was given in conjunction with daclizumab 1 mg/kg or placebo on study days 1, 4, 8, and weekly as long as clinically indicated. The groups were balanced for clinical characteristics. GVHD response rates by study day 42 were similar (53% vs 51%; P =.85). The study was halted after a planned interim analysis showed a significantly worse 100-day survival in the group receiving corticosteroids plus daclizumab (77% vs 94%; P =.02). Overall survival at 1 year was also inferior in the combination arm (29% vs 60%; P =.002). Both relapse- and GVHD-related mortality contributed to the increased mortality in the combination group. The combination of corticosteroids and daclizumab should not be used as initial therapy of acute GVHD.