Brochoalveolar lavage (BAL) were performed in 28 patients with sarcoidosis and in 31 normal subjects. In control subjects, the numbers of mononuclear cells and macrophages in smokers were significantly increased in comparison to nonsmokers (p<0.001 in each cases), but the numbers of lymphocytes were not.In both smoking and nonsmoking untreated sarcoid patients, the proportion and number of lymphocytes were significantly increased compared to corresponding controls (p<0.05, p<0.001). The number of lymphocytes in patients not receiving prednisolone were not significantly increased than patients who were receiving prednisolone. No difference in numbers of lymphocytes was found between smoker and nonsmoker patients. BAL lymphocytes were identified as T lymphocytes (88.9±6.2%). Furthermore, untreated patients had significantly higher percentages of OKT-4 (+) T helper cells and significantly lower OKT8 (+) T suppresser cells within the alveolar lymphocytes population than that of normal nonsmokers (p<0.01 in each cases). Alveolar lymphocytosis is significantly correlated with the activity of lymphocyte blastogenesis induced by Propionibacterium acnes (p<0.01), and the ratio of OKT-4 (+) cells to OKT-8 (+) cells correlated with the activity of serum angiotensin-converting enzyme (p<0.05). However, neither the radiological stage nor the degree of Gallium-67 uptake in lung parenchyma was related to the lymphocyte number and the ratio of OKT-4/OKT-8 in BAL fluids.The lymphocytosis of the bronchoalveolar space indicates the disease activity at the site of pulmonary space, and Propionibacterium acnes may play some role in the induction of the pulmonary lymphocytosis in sarcoidosis patients.