The benefits of oral prophylaxis for neutropenia have remained controversial up to now. We evaluated retrospectively the effect of antibiotic prophylaxis with ciprofloxacin and penicillin on the prevention of bacterial infections in 112 cases of prolonged neutropenia in adult patients treated for haematological malignancies. 41 patients received prophylaxis between December 1993 and November 1994 while 71 patients did not receive prophylaxis between December 1994 and November 1995. There were no significant differences between groups in age, sex, type or stage of haemopathy, type of chemotherapy and duration of neutropenia. The antibiotic prophylaxis reduced the number of overall infections (p = 0.05) and the number of gram-negative bacteraemias (p = 0.02). The median time to the onset of fever, the duration of fever, the duration of antibiotic treatment, the duration of hospitalization or admission to the intensive care unit, the number of serious complications or death were not influenced by antibiotic prophylaxis. The prophylaxis did not reduce the overall incidence of bacteraemia, of clinically documented infections or of fever of unknown origin. This retrospective study confirms that oral prophylaxis with ciprofloxacin and penicillin decreases the incidence of infections and, in particular, of gram-negative bacteraemia, but does not modify the overall morbidity and mortality in our patients. In view of the risk of emergence of bacterial resistance, these data do not support the routine use of oral antibiotic prophylaxis in neutropenic patients with haematological malignancies.