Concentrations of telithromycin were measured in plasma, bronchial mucosa (BM), epithelial lining fluid (ELF) and alveolar macrophages (AM) following multiple oral doses. Concentrations were determined using a microbiological assay. There were 20 subjects in the study, allocated to three nominal time periods: 2, 12 and 24 h. Mean concentrations in plasma, BM, ELF and AM for 2, 12 and 24 h were as follows: 2 h, 1.86 mg/L, 3.88 mg/kg, 14.89 mg/L and 69.32 mg/L; 12 h, 0.23 mg/L, 1.41 mg/kg, 3.27 mg/L and 318.1 mg/L; and 24 h, 0.08 mg/L, 0.78 mg/kg, 0.97 mg/L and 161.57 mg/L. These concentrations of telithromycin in BM and ELF exceeded for 24 h the mean MIC90s of the common respiratory pathogens Streptococcus pneumoniae (0.12 mg/L) and Moraxella catarrhalis (0.03 mg/L), as well as the atypical microorganism Mycoplasma pneumoniae (0.001 mg/L), and suggest that telithromycin may be effective for the treatment of community-acquired pneumonia and chronic obstructive pulmonary disease.