BACKGROUND: Macrophages are involved in asthma, but their pulmonary turnover is unknown. We compared the ability of bronchoalveolar lavage (BAL) and bronchial macrophages to proliferate in normal subjects and patients with asthma. METHODS: BAL cells from eight patients with asthma and eight normal volunteers were separated with a discontinuous Percoll gradient (Pharmacia Fine Chemicals, Uppsala, Sweden). In a first experiment, nuclei of each alveolar macrophage (AM) fraction, stained with propidium iodide, were analyzed for DNA content with a flow cytometer, and the proportions of cells in the G0/G1, S, and G2 + M phases were determined. In a second experiment, expression of Ki-67-related antigen was sought on AMs by immunocytochemistry. Macrophages from 10 patients with asthma and 10 normal volunteers were studied in biopsy specimens by means of immunohistochemistry with a panmacrophage monoclonal antibody (HAM-56) and a monoclonal antibody against proliferating cell nuclear antigen. RESULTS: The proportions of BAL AMs in the different phases of the cell cycle were similar in normal subjects and patients with asthma for all fractions, and the percentage of cells in S and G2 +/- M phases ranged from 7.3% to 11.3%. Under 1% of BAL AMs expressed Ki-67-related antigen. None of the macrophages present in the biopsy specimens expressed proliferating cell nuclear antigen. CONCLUSIONS: This study does not indicate that an important source of airway macrophages is local proliferation.