The effectiveness and safety of cefmenoxime (CMX) in the treatment of respiratory tract infections were evaluated, mainly in relation to the appearance of hemorrhagic tendency. Out of 80 patients treated in this study, 57 were treated with CMX alone, and an effective rate was determined to be 75.4%. As for a tendency toward hemorrhage, none of the patients clinically exhibited a hemorrhagic tendency, while the prolongation of prothrombin time (PT) and/or activated partial thromboplastin time (APTT) was seen in 3 patients (3.8%), who were all at ages over 63. The prolongation of APTT was clearly related to CMX in 1 patient. Although the causal relation between CMX and the prolongation of PT or APTT was unclear in the remaining 2 patients because they had severe primary diseases (lung cancer and respiratory failure due to chronic obstructive lung disease in addition to severe hepatic disorder and received combination treatment with anticancer agents or other antibiotics), CMX might have a role in causing these phenomena. Even though none of the patients showed a hemorrhagic tendency clinically arousing problems, we should be careful in using CMX in the treatment of the aged and patients in poor general conditions because PT and/or APTT was observed to prolong with the use of CMX in some patients.