Bronchoalveolar lavage (BAL) may have a potential role in contributing to a more precise definition of COPD disorders, but at present little is known about the cellular and biochemical changes that occur in BAL in the different stages of COPD. On the contrary, BAL features due to smoking habits, a well-known risk factor for COPD, have been widely investigated. We submitted to BAL 15 normal nonsmokers, 15 asymptomatic smokers and 11 smokers affected by chronic bronchitis. In this latter group BAL fluid recovery was significantly reduced and cellularity increased, but less prominently than in asymptomatic smokers. The CD4/CD8 ratio was significantly decreased in smokers with and without bronchitis, the CD8 percentage being positively correlated with the smoking history. NK cells were decreased in patients with chronic bronchitis. BAL neutrophils were increased in both smoker groups and a correlation was seen with smoking history and degree of airflow obstruction. Neutrophils are markedly involved in the oxidation of BAL proteins, as we could determine with the evaluation of the methionine sulphoxide/methionine ratio in BAL fluids. This finding may be relevant to better understand COPD pathogenesis and progression.