• The concentration of glutamic oxalacetic aminopherase in the serum of a series of normal subjects was found to be 10 to 45 units per milliliter. Values within this range were also found in a series of patients with a great variety of cardiac diseases except acute myocardial infarction; in nine patients with this condition the serum aminopherase reached values from 3 to 12 times the normal. Slight elevations were noted in elderly patients with prolonged shock in whom there was no demonstrable acute myocardial injury, and one patient with acute rheumatic pancarditis also gave high figures. High aminopherase values, however, sometimes had extracardiac causes. In two instances they accompanied the necrosis of skeletal muscle resulting from vascular disease of the lower extremities. In 20 patients with jaundice of varying etiology high figures were also obtained, and they seemed to be in proportion to the amount of cellular necrosis found in liver biopsy specimens. Extreme elevation occurred in one patient with infarction of the liver.