The frequency of infection in recipients of allogeneic bone marrow transplants (BMT) who received oral new quinolones (NQ) was compared with that in BMT recipients who were given oral vancomycin/tobramycin (V/T). Between 1984 and 1997, our hospital treated 79 patients with V/T and 90 patients with NQ. Number of febrile days, duration of intravenous antibiotics administration, and frequency of documented infections were statistically the same for both groups. However, the frequency of grampositive bacterial infections, especially staphylococcal infections, was slightly higher in patients receiving NQ than in patients receiving V/T (p = 0.12). Of the patients who received NQ, those who underwent unrelated donor BMT procedures were generally febrile for slightly longer periods than those who underwent related donor BMT procedures (p = 0.10). These results suggest that oral NQ is as effective as oral V/T for the prevention of serious gramnegative bacterial infections in patients who undergo BMTs.