Serum angiotensin converting enzyme levels were measured in 184 subjects having either MM, MZ, ZZ, or MS Pi-types of alpha 1-antitrypsin. Elevated angiotensin converting enzyme levels were detected in 31 percent of the patients with the MZ Pi-type, 20 percent of the patients with the ZZ Pi-type, and 20 percent of the patients with the MS Pi-type compared with 1.33 percent of those with normal MM Pi-type. The mean serum angiotensin converting enzyme levels were also significantly higher in those with the MZ, ZZ, and MS Pi-types. Multiple family members of two families were found to have both the Z variant and angiotensin converting enzyme elevations, suggesting the possibility of a genetic linkage. Alpha 1-antitrypsin deficiency must be added to the list of disease states potentially associated with elevated serum angiotensin converting enzyme levels.