Brucellosis is one of the leading diseases in the differential diagnosis of fever of unknown origin in some parts of the world. It can lead to treatment failure because of slow growth in blood cultures and late appearance of signs and symptoms in patients with febrile neutropenia who were unresponsive to empirical antibiotic treatment. During the last year in our oncology unit adjuvant chemotherapy was given to 3 patients with breast (n=l) and stomach cancer (n=2) and febrile neutropenia was seen after the first course of chemotherapy (cyclophosphamide, methotrexate, 5-fluorouracil, etoposide, Adriamycin, and cisplatin) in all 3 patients. Cefepime and amikacin were commenced but the fever continued. Prior to antifungal treatment, the patients were re-evaluated because of the history of unpasteurized milk ingestion without overt signs and symptoms. Serum agglutination tests of brucellosis were performed and were 1:640 in two patients and 1:320 in the third. Brucella melitensis was identified only in one case although multiple blood cultures were taken from all 3 patients. Empiric antibiotic treatment was stopped and streptomycin 1 g/day (10 days), doxycycline 200 mg/day (28 days), trimethoprim 320 mg and sulfamethoxazole 1600 mg/day (28 days) were given. Although neutropenia continued, fever subsided in 3 days. Due to high incidence of brucellosis in some geographic areas, especially in the Middle East, brucellosis should be kept in mind in the differential diagnosis of febrile neutropenia.