Chronic obstructive pulmonary disease (COPD) patients have an increased number of T cells within their lungs. It is unknown whether these T cells, remain there forever or if there is a continuous turnover from the blood. In the adult, there is a significant T lymphocytopoiesis from the thymus producing cells known as recent thymic emigrants (RTEs). T cell receptor excision circles (TREC) are a marker of RTEs. We investigated the number of TREC in blood from patients with untreated stable, mild to moderate COPD (n=6) compared with age-matched smokers with normal lung function (n=6) and nonsmokers (n=8). The results showed variable expression of TREC in each subject group and no significant difference between TREC expression in any group of subjects. Changes in T-cell numbers in the lung of stable COPD patients, may reflect prolonged survival or proliferation of these cells within the lung rather than continuous recruitment from the blood.