Empiric therapy for febrile granulocytopenic patients is mandatory, but whether monotherapy is a safe alternative and whether fluoroquinolones are useful agents for this indication are still controversial issues. The use of monotherapy with intravenous ciprofloxacin (200 to 300 mg every 12 h) was evaluated against combined therapy with piperacillin plus amikacin in febrile granulocytopenic patients with solid tumor or lymphoma. The study was discontinued prematurely because patients treated with ciprofloxacin had a significantly lower overall success rate than patients treated with piperacillin plus amikacin (31 of 48 patients [65%] versus 48 of 53 patients [91%], P = 0.002). Patients with gram-positive coccal bacteremia had a particularly poor outcome: therapy failed for six of eight patients (75%) treated with ciprofloxacin, while therapy failed for none of four patients treated with piperacillin plus amikacin. Death from primary infection during initially randomized protocol therapy occurred in 7 of 48 patients (14.5%) treated with ciprofloxacin and in 3 of 53 (6%) treated with piperacillin plus amikacin. This study does not support the use of this dose of intravenous ciprofloxacin as empiric monotherapy for fever in granulocytopenic patients.