The aim of the present study was to obtain clinical experience with the use of high-dose ciprofloxacin as monotherapy for the treatment of febrile neutropenia episodes (granulocyte count, <500/mm(3)) compared to a standard regimen and to clarify whether ciprofloxacin administration may be switched to the oral route. In a prospective randomized study ciprofloxacin was given at 400 mg three times a day (t.i.d.) for at least 72 h followed by oral administration at 750 mg twice a day (b.i.d). That regimen was compared with ceftazidime given intravenously at 2 g t.i.d. plus amikacin given intravenously at 500 mg b.i.d. The frequency of successful clinical response without modification at the end of therapy was almost identical for ciprofloxacin (50% [62 of 124 patients]) compared with that for ceftazidime plus amikacin (50.8% [62 of 122 patients]) in an intent-to-treat analysis; the frequencies were 48.3% (57 of 118 patients) versus 49.6% (56 of 113 patients), respectively, in a per-protocol analysis (P values for one-sided equivalence, 0.0485 and 0.0516, respectively; delta = 10%), with no significant differences among patients with bacteremia and other microbiologically or clinically documented infections and fever of unknown origin. For 82 (66.1%) patients, it was possible to switch from parenteral ciprofloxacin to the oral ciprofloxacin, and the response was successful for 61 (74.4%) patients. The efficacies of the regimens against streptococcal bacteremias were 16.6% (one of six patients) for the ciprofloxacin group and 33.3% (one of three patients) for the combination group (it was not statistically significant), with one breakthrough streptococcal bacteremia observed among the ciprofloxacin-treated patients. Adverse events were mostly self-limited and were observed in 27 (20.6%) ciprofloxacin-treated patients and 26 (19.7%) patients who were receiving the combination. This study demonstrates that high-dose ciprofloxacin given intravenously for at least 3 days and then by the oral route is therapeutically equivalent to the routine regimen of intraveneous ceftazidime plus amikacin even in febrile patients with severe neutropenia (polymorphonuclear leukocyte count, <100 mm(3)). However, it is very important that before an empirical therapy is chosen each hospital determine bacteriologic predominance and perform resistance surveillance.