In 13 cases of pneumonectomy, we have studied the concentration of TMP-SMZ in tissue and serum, after three days of treatment. Four hours after TMP-SMZ injection, the tissue's samples obtained from crushed and mixed ; the dosages were performed by a microbiological assay. As we previously described in bronchial secretions : the lung penetration of TMP is important ; the tissue concentrations were higher than in serum ; the diffusion of SMZ is low. The ratio of TMP to SMZ were diffusion of SMZ is low. The ratio of TMP to SMZ were different in serum and tissue, but the antibacterial activity is not affected in vitro by the value's modification.