In a prospective, randomized, controlled trial, we compared sulbactam/cefoperazone with imipenem as empirical monotherapy for febrile, granulocytopenic patients; 101 patients received sulbactam/cefoperazone (2 g/4 g every 12 hours) and 102 patients received imipenem (500 mg every 6 hours). Documented infections were present in 40% of patients treated with sulbactam/cefoperazone (40 of 101) and in 39% of patients receiving imipenem (40 of 102). The number of pretherapy gram-positive pathogens (52 isolates) was twice the number of pretherapy gram-negative pathogens (26 isolates). The overall favorable clinical response rates for sulbactam/cefoperazone (91 of 103 patients, or 88%) and imipenem (84 of 104 patients, or 81%) were similar. Both drugs were generally well tolerated. However, diarrhea occurred more often in patients treated with sulbactam/cefoperazone (31 of 101 patients, or 31%, vs. 15 of 102 patients, or 15%; P = .007), while seizures developed only in patients receiving imipenem (0 of 101 patients vs. 3 of 102 patients, or 3%). Superinfections developed in 16% of patients in both study groups but were infrequently caused by beta-lactam-resistant gram-negative bacilli (two cases with sulbactam/cefoperazone therapy and six cases with imipenem). These results support the efficacy and safety of either sulbactam/cefoperazone or imipenem as empirical monotherapy for febrile granulocytopenic patients.