Glutamic-oxaloacetic transaminase is increased in the serum following damage to either liver or muscle cells. Glutamic-pyruvic transaminase is found in relatively high concentration in the liver. In this investigation of an assortment of liver and gastrointestinal diseases, it was found that both enzymes became elevated following damage to liver cells. Damage to muscle cells alone, as in myocardial infarction, did not produce a significant elevation of glutamic-pyruvic transaminase. Thus the simultaneous determinations of glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase may be of value in differentiation between diseases with damage to liver cells and diseases causing necrosis of muscle.