The inflammation of the lungs in chronic obstructive pulmonary disease (COPD) is characterised by increased numbers of macrophages, neutrophils and T-cells. Decline in lung function in these patients has been correlated to the number of CD8+ T-cells present in the lung as well as to a decline in the ratio of CD4+/CD8+ T-cells. Although systemic components are likely to be present, circulating lymphocyte populations in COPD patients have not been well characterised. This study aimed at correlating lung function to expression of five different T-cell activation markers on peripheral blood CD4+ and CD8+ T-cells in COPD patients and matched smokers. Furthermore, proportions of lymphocyte populations and degree of systemic T-cell activation in COPD patients were compared to that in smokers and never-smokers. Peripheral blood lymphocytes from six never-smokers, eight smokers and 17 smokers with COPD were analysed using flowcytometry. The number of lymphocytes per millilitre was higher in smokers than in never-smokers. No differences were found between the three groups in regard to proportions of lymphocyte populations, but the number of CD4+ T-cells in smokers was higher than in both never-smokers and COPD patients. The degree of T-cell activation was similar in all patient groups; however, a clear correlation between CD69 expression on CD4+ T-cells and lung function (FEV₁% of predicted) was found when examining current smokers, with or without COPD. Elevated numbers of CD69+ CD4+ T-cells in blood thus seem to be protective against airway obstruction in smokers while still exposed to cigarette smoke, the main inducer of COPD.