Serum angiotensin-converting enzyme (ACE) activity was measured in 18 healthy controls, 26 patients with active sarcoidosis, 13 patients with inactive sarcoidosis and seven patients with extensive tuberculosis. The serum ACE activity showed no significant difference between male and female in the control or sarcoidosis groups. There was no correlation between ACE activity and age except in the female active-sarcoid group. ACE activity in the active-sarcoid group was significantly higher than in the control, inactive-sarcoid and tuberculosis groups. The ACE activities at Stages I, II and III of the disease were not significantly different.