Limited data on the cellular and immunocytologic characteristics of bronchoalveolar lavage (BAL) fluid in pulmonary tuberculosis have been reported. We therefore studied 40 patients with active disease. BAL fluid differential cell counts and lymphocyte subsets were determined. The findings were compared with data from 47 patients with active sarcoidosis and 30 healthy control subjects. The proportion of lymphocytes was increased in both diseases (p < 0.001 versus control subjects) but with no difference compared to one another. The CD4/CD8 ratio was normal in 33 of 40 patients with pulmonary tuberculosis in contrast to sarcoidosis, with an increased ratio in 33 of 47 patients. HLA-DR(+) T lymphocytes were significantly increased in both pulmonary tuberculosis and sarcoidosis (p < 0.05 versus control group). The proportion of CD57(+) lymphocytes was normal in all study groups. We conclude that pulmonary tuberculosis and sarcoidosis are characterized by an increased percentage of lymphocytes in BAL fluid with a similar proportion of activated T cells. In contrast to active sarcoidosis, in which an elevated CD4/CD8 ratio is characteristic, in the majority of pulmonary tuberculosis patients the CD4/CD8 ratio is within the normal range.