The mechanisms behind airway inflammation in chronic obstructive pulmonary disease (COPD) are still not well understood. Here we investigated lymphocyte subtypes in bronchoalveolar lavage fluid, likely to be involved in the pathogenesis of COPD, as well as exploring the effect of smoking cessation. Differential cell counts and T cell subsets were determined in BAL fluid from nineteen individuals with stable COPD (seven smokers, twelve ex-smokers) compared to twelve age-matched never-smokers and thirteen smoking-matched smokers with normal lung function. COPD-patients had higher percentages of airway CD8(+) T cells compared to never-smokers. An increased population of CD4(+) T cells expressed high levels of CD25 in smokers and COPD patients compared to never-smokers, suggesting the presence of regulatory T cells. As the T cell populations in smokers with normal lung function and COPD-patients were similar, the impact of current smoking in COPD was addressed in a subgroup analysis. Activation of CD8(+) T cells was found regardless of smoking habits. In contrast, the enhanced expression of gamma/delta T cells, was mainly associated with current smoking, whilst the increase in T regulatory cells appeared related to both smoking and COPD. Regardless of smoking habits, CD8(+) T cell activation was found in COPD, supporting the contention that this T cell subset may play a role in the pathogenesis of COPD. As CD8(+) T cells coexist with immunoregulatory CD4(+) T cells in airways of COPD patients, it is likely that both cytotoxic T-cell responses and immunosuppressive mechanisms may be of importance in COPD pathogenesis.