Seventeen breast cancer patients with tumor-associated fever are described. All other potential causes of fever were excluded in each patient, and it was diagnosis of exclusion. Fever was the first manifestation of recurrence in seven patients. In ten patients fever developed in association with new sites of metastases or progression of disease. New sites of metastasis in most of the patients were liver, bone marrow, or lungs. Seven patients had metastatic disease that responded to chemotherapy or hormonal therapy; fever subsided in only these patients (responding group). In nine patients neither tumor nor fever showed response to systemic treatment (nonresponding group). Overall survival after onset of fever was better in the responding group than nonresponding group.