We present two cases of malignant lymphoma that developed a high fever that eventually reached an extremely high 38.9 degrees C. The C-reactive protein( CRP) elevation also climbed to a very high 12.2 mg/dl after treatment with granulocyte colony-stimulating factor (G-CSF). In the one case, after stem cells were mobilized with CHASER therapy (cyclophosphamide, cytarabine, etoposide, dexamethasone and rituximab) followed by G-CSF (filgrastim 600 microg/day) subcutaneous daily, the serum CRP level rose to a maximum of 5.6 mg/dl, with a maximum fever elevation of 38.9 degrees C. In the other case, after the subject was given CHASE therapy followed by subcutaneous treatment with G-CSF (filgrastim 75 microg/day) daily, the maximum serum CRP level was 12.2 mg/dl along with a maximum fever of 38.9 degrees C. Although no infection was found in either case, multiple antibacterial agents were ineffective;after discontinuation of G-CSF, fever dissipated and the serum CRP level became negative. G-CSF induces the proliferation and differentiation of neutrophils and also causes the mobilization of mature neutrophils from hematopoietic tissues. With the increasing propensity to G-CSF, we must keep in mind the possibility of such adverse reactions so as to serve the overall best interests of the patient.