The efficacy and the safety of a combination regimen using cefbuperazone (CBPZ) and amikacin (AMK) were evaluated in severe infections in patients with hematological diseases. Twenty two patients were subjected to this combination therapy; among these, 18 patients were evaluable for the effectiveness. They included 9 cases of leukemia, 5 cases of malignant lymphoma, 2 cases of aplastic anemia, and 2 cases of angio-immunoblastic lymphadenopathy with dysproteinemia. Excellent responses were obtained in 5 patients and good responses in 5 patients, with a total effectiveness of 55.6%. Efficacy rates for individual types of infections were; 2/2 in sepsis, 6/14, or 42.9% in suspected sepsis, 1/1 in urinary tract infection, and and 1/1 in upper respiratory infection. The combination treatment was also effective in 4 of 6 cases in which neutrophil counts were less than 500/mm3 prior to therapy. Side effects were observed in only one patient. Mild proteinuria occurred in a 80-year-old male in 6 days after the regimen was started, but was not serious. These results indicate that a combination of CBPZ and AMK is safe and effective for the treatment of infections even in patients with compromised immunodefenses.