Angiotensin converting enzyme (ACE) (dipeptidyl carboxypeptidase; peptidyldipeptide hydrolase, EC 3.4.15.1) was localized in epithelioid and giant cells within ACE-rich sarcoidosis granulomas, but not control granulomas, by immunofluorescence by using a rabbit anti-human ACE immunoglobulin for localization and fluorescein-labeled goat anti-rabbit immunoglobulin for detection. ACE was frequently not detected in the very central epithelioid cells, perhaps due to a paucity of cellular or molecular stimulatory interaction in this region. The results suggest that marked elevation of ACE in the granulomas and often in the serum in sarcoidosis may be due to intense induction of ACE in most epithelioid and giant cells of the sarcoidosis granulomas.