In a study undertaken to evaluate fluoroquinolone prophylaxis in afebrile granulocytopenic patients, an unexpected association between chemotherapy schedule and a later development of bacteremia--during the subsequent febrile neutropenic episodes--was found. Twenty five febrile neutropenic episodes consecutive to chemotherapy for acute leukemia were studied. Patients received either etoposide and mitoxantrone or citarabine--in standard, intermediate or high doses--combined with daunomicin or mitoxantrone. Microbiologic data analysis showed an increased incidence of bacteremia with combined anthracycline and intermediate or high dose citarabine administration, when compared to etoposide and mitoxantrone use (p = 0.000387). Both groups developed similarly fast and severe neutropenias and equivalent grades of digestive mucositis. Chemotherapy schedule was the only factor associated with a consecutive bacteremia--or not--during the subsequent neutropenic episode. We conclude that effects other than bone marrow aplasia and digestive mucositis may be relevant in infectious susceptibility induced by cytostatic drugs.