Therapeutic effects on cefmenoxime hemihydrochloride (CMX, Bestcall), a new synthetic cephem antibiotic, were examined in the treatment of various infections complicated with hematological diseases. The number of patients treated with CMX was 37 including 5 cases of sepsis or suspected sepsis, 14 cases of pneumonia or suspected pneumonia, 5 cases of upper respiratory diseases, 2 cases of urinary tract infections and 11 cases of other infections. All of these infections were complicated with hematological diseases: Acute leukemia, 13 cases; chronic myelocytic leukemia, 1 case; adult T cell leukemia, 3 cases; malignant lymphoma, 8 cases; Hodgkin's disease, 2 cases and myeloma, 3 cases. CMX were administered by a single intravenous injection or by a drip infusion. The dose was between 2 and 6 grams per day. Good to excellent clinical results were obtained in 25 out of 37 cases, total effective rate of 67.6%. No clinical side effects or abnormal laboratory findings attributable to CMX were observed except for light diarrhea in 2 cases. By the clinical investigation, it was demonstrated that CMX was one of safe and effective antibiotics for treating infections in the compromised hosts complicated with hematological diseases.