An 80-year-old man presented to the internist with fever, fatigue and leukocytosis up to 66.8 x 10(3)/microl. Although a chronic myelogenous leukemia was initially suspected, he was diagnosed as metastatic bone marrow tumor with bone marrow necrosis from primary prostate cancer on the basis of the clinical and pathological findings. The serum concentrations of IL-6 and TNF-alpha were mildly elevated to 65.0 pg/ml and, 54.0 pg/ml respectively. It is probable that these humoral factors were partially responsible for the leukemoid reaction although other factors induced by the bone marrow necrosis with bone marrow metastasis of prostate cancer are also likely involved.