Exogenous pyrogens induce several cytokines which activate immune responses, and produce fever. In Japan, febrile neutropenia is defined as having an axillary temperature of>37. 5°C, and neutropenia showing an absolute neutrophil count (ANC)of<500 cells/mL or an ANC that is expected to reduce to<500 cells/mL during the next 48 hours. Signs and symptoms of inflammation are often attenuated or absent in neutropenic patients. Therefore, careful physical examination is required to detect subtle symptoms and signs of infection. As an initial assessment, laboratory tests should include the following: a ) complete blood cell count with differential leukocyte count and platelet count, b ) measurement of serum levels of creatinine, electrolytes, and hepatic transaminase enzymes, c ) serologic assay for fungal infection, and d ) at least 2 sets of blood cultures. Radiographical approaches are also important for detecting the focus of infection. Proper risk classification should be performed using the Multinational Association for Supportive Care in Cancer(MASCC)scoring system to distinguish high-risk and low-risk patients with febrile neutropenia.