Angiotensin-converting enzyme (ACE) was detected by indirect immunofluorescence examination. ACE was present in the cytoplasm of epithelioid cells in granulomas from 38 of 39 patients who had clinical sarcoidosis but not in any of 37 nonsarcoid granulomas, normal lymph nodes, or splenic controls. Intensity of staining with ACE antiserum was inversely proportional to the degree of fibrosis and was significantly less intense in fibrotic granulomas. The detection of ACE appears to be a distinct aid in establishing a definitive tissue diagnosis of sarcoidosis.