Objective: This study was designed to measure the concentrations of linezolid in bronchial mucosa, pulmonary macrophages and epithelial lining fluid and to compare them with simultaneous blood levels. Methods: Ten adult patients undergoing bronchoscopy for diagnostic purposes were given oral linezolid at a dosage of 600 mg twice a day for a total of six doses. Patients with active lung infection were excluded from the study. Flexible bronchoscopy was carried out between 2 and 8 h after the last dose of linezolid. Bronchial biopsies and bronchoalveolar lavage were carried out and a simultaneous blood sample obtained. Linezolid levels were measured using high-performance liquid chromatography (HPLC). Results: Mean concentrations of linezolid were 13.4 mg/L in serum, 10.7 mg/kg in mucosa, 8.1 mg/L in alveolar macrophages and 25.1 mg/L in epithelial lining fluid. The mean site/serum concentration ratios were 0.79 for bronchial mucosa, 0.71 for macrophages and 8.35 for epithelial lining fluid. Conclusions: The MIC90 (≤4 mg/L) of linezolid for Staphylococcus aureus and Streptococcus pneumoniae was exceeded in serum and bronchial mucosa in all subjects, in epithelial lining fluid in nine subjects and in macrophages in six subjects.