Hemophagocytic lymphohistiocytosis (HLH) is a rare and severe inflammatory disorder marked by abnormal cytotoxic T and natural killer cell activity, resulting in impaired clearance of pathogen, excessive cytokine production, and continued immune system activation. Soluble IL-2 receptor (sIL-2R or sCD25) is typically elevated in HLH and can serve as a marker of disease activity, although its role in the pathophysiology of the disease is unclear. Here we present a case of an adult patient with steroid-dependent HLH who was treated successfully with daclizumab, a monoclonal anti-CD25 antibody, allowing successful withdrawal of steroid therapy without an increase in symptoms. Am. J. Hematol., 2008. © 2008 Wiley-Liss, Inc.