In a prospective study, 157 patients with prolonged aplasia (PMN less than 500/mm3 during more than 21 days), hospitalized in a protected environment unit, were randomly assigned to receive ceftazidime alone or cefotaxime + tobramycin for initial febrile episodes. Age, sex, underlying diseases, duration of neutropenia, digestive decontamination regimen, clinical and microbiological characteristics of infections were similar in the two groups. Patients were evaluated for their initial response to antibiotics (defervescence in 48 hours, maintained 7 days) and long term response (prevention of another infection during aplasia). The overall initial response to ceftazidime was 48/71 (68 per cent) and to cefotaxime + tobramycin 55/86 (64 per cent). The long term response to ceftazidime was 33/71 (46.5 per cent) and to cefotaxime + tobramycin 31/86 (36 per cent). In conclusion, ceftazidime alone was as effective as cefotaxime + tobramycin in the first line treatment of febrile episodes in neutropenic patients.