We evaluated the efficacy of piperacillin-tazobactam monotherapy as empiric therapy of fever in acute leukemia patients in a total of 80 consecutive febrile episodes. The overall success rate was 75% with success without modification in 34% (afebrile at 72 h) and an overall death rate of 10%. No significant differences were seen in correlation between clinical outcome and phases of underlying disease. The success without modification was higher in patients with fever of unknown origin (FUO) than in those with documented infections (47% and 25% respectively). There were no significant differences in correlations between clinical response and degree of neutropenia. Our study suggests that empirical first-line monotherapy with piperacillin-tazobactam may be a reasonable option in patients with acute leukaemia, although in documented infections the response is frequently inadequate.