Résumé : The practical procedures of digestive tract decontamination and prophylaxis of bacterial infection in granulocytopenic patients are debated. Fluoroquinolones are active against Gram-negative bacilli and have few side-effects. Pefloxacin was administered prophylactically to patients with cancer and granulocytopenia. None of them developed Gram-negative septicaemia, but 2 cases of streptococcal septicaemia were observed. The drug was well tolerated by all patients except one. Studies are currently in progress to try to reduce the incidence of septicaemia caused by Gram-positive cocci, using pefloxacin combined with penicillin.