BACKGROUND: Therapy with an aminoglycoside and a beta-lactam remains common empirical therapy for febrile neutropenic patients. Concerns of aminoglycoside-induced ototoxicity and nephrotoxicity have led to studies of alternate regimens. OBJECTIVE: To determine whether ciprofloxacin-piperacillin is equivalent to tobramycin-piperacillin as empirical therapy for neutropenic fever. DESIGN: Randomized, double-blind multicenter trial. SETTING: Seven U.S. university-affiliated hospitals and one private research center. PATIENTS: Febrile (temperature >/= 38 degrees C), neutropenic (neutrophil level < 1 x 10(9) cells/L) hospitalized patients who had leukemia, lymphoma, or solid tumors, or were undergoing bone marrow transplantation. INTERVENTIONS: Patients received piperacillin, 50 mg/kg of body weight intravenously every 4 hours, and ciprofloxacin, 400 mg intravenously every 8 hours, or tobramycin, 2 mg/kg intravenously every 8 hours. MEASUREMENTS: Success was defined as resolution of infection and previously positive cultures without the need to give additional antimicrobial agents. RESULTS: 543 febrile episodes were evaluated, of which 471 were clinically evaluable (234 in the ciprofloxacin-piperacillin group and 237 in the tobramycin-piperacillin group). Success rates in the ciprofloxacin-piperacillin group (63 of 234 febrile episodes) and tobramycin-piperacillin group (52 of 237 episodes) were similar (27% vs. 22%, respectively; difference, 5.0 percentage points [95% CI, -2.3 to 12.8 percentage points]), as was survival (96.2% of patients receiving ciprofloxacin-piperacillin versus 94.1% of patients receiving tobramycin-piperacillin; difference, 2.1 percentage points [CI, -2.2 to 6.4 percentage points]). Additions to the initial antimicrobial regimen were the most common reason for treatment failure in both groups (accounting for 67% of failures in the ciprofloxacin-piperacillin group and 72% in the tobramycin-piperacillin group; difference, 5.0 percentage points [CI, -13.8 to 3.7 percentage points]). Fevers resolved faster in patients receiving ciprofloxacin-piperacillin than in patients receiving tobramycin-piperacillin (mean, 5 vs. 6 days) (P = 0.005). No significant differences in adverse events or toxicity were noted (P = 0.083). CONCLUSION: Ciprofloxacin-piperacillin is as safe and effective as tobramycin-piperacillin for empirical therapy of neutropenic fever.