Surveillance cultures of the stool were obtained from 55 patients with hematological malignancies, who have been receiving norfloxacin or tosufloxacin during their neutropenic periods, from May, 1991 to September, 1992. Cultures were performed using 5% blood agar with piperacillin 300 micrograms/ml and amikacin 20 micrograms/ml and bacteria resistant to these antibiotics were analyzed further. Thirty-four over 55 patients were positive for enterococci and 22 strains of 23 examined were Enterococcus faecium. They are resistant to quinolones, aminoglycosides, cephalosporins and penicillins but not to vancomycin. Eighteen of them were also resistant to high-dose gentamicin. Appropriate measures should be used to prevent intrahospital spread of these resistant isolates.