Patients with active pulmonary sarcoidosis underwent bronchoalveolar lavage, gallium scan, and serum angiotensin-converting enzyme (ACE) level determination prior to treatment with corticosteroids. Pulmonary function was tested before and after therapy. Increase in vital capacity after treatment ranged from 40 to 1,030 ml; 12 of the 16 patients studied had an increase of more than 200 ml. There was a close correlation between the percentage uptake of gallium scan and the increase of the vital capacity after therapy (r = 0.95, p less than 0.01). There was no relationship between the percentage of lymphocytes obtained on lavage and the changes in vital capacity with therapy (r = 0.05). There was a positive correlation between the changes in vital capacity and the ratio of T4(+):T8(+)lymphocytes (r = 0.62, p less than 0.05) and number of T4 (+) lymphocytes (r = 0.92, p less than 0.01) in the bronchoalveolar fluid. There was a low correlation between the pretreatment ACE level and the change in vital capacity (r = 0.368, p greater than 0.05).