Episodes of fever are very common in patients undergoing intensive chemotherapy treatment for malignant hematological disease. More than 80% of patients experience one or more episodes of fever after their first cycle of chemotherapy. Only 20-30% of these patients have a clinically documented focus and mostly include infections of skin, intestinal tract and lung, while at most 10-25% of these patients have microbiologically proven bacteremia during these episodes. Patients with malignant hematological diseases and intensive chemotherapy induced neutropenia are extremely prone to overwhelming bacterial infections. Therefore, empirical antibiotic treatment is initiated at the first occurrence of fever, even if no apparent cause for the fever is evident. Most protocols advice treatment with very broad-spectrum antibiotics, mostly anti-pseudomonal carbapenems or fourth generation anti-pseudomonal cephalosporins.