Twenty patients who were performed pulmonary resection for the disease of the lung were administered 2 g of cefmenoxime (CMX) intravenously during the operation. The CMX levels in serum, lung tissue and thoracic muscle were measured by agar-well technique. The CMX levels in lung tissue and thoracic muscle were higher than the MIC80 of CMX for Klebsiella pneumoniae, Haemophilus influenzae and Streptococcus pneumoniae which were commonly as isolated causative organisms from the patients with pulmonary infection. These results indicate that CMX will be useful agent for the prevention and treatment of pulmonary infection.