1. (1) Marked inhibition of GOT by low concentrations of added oxaloacetate was demonstrated. This supports a previous conclusion that GOT was inhibited by oxaloacetate produced during the reaction. The inhibition was more marked with one isoenzyme GOT II, than with the other, GOT I. 2. (2) It was shown that the reitman and frankel method, in which the oxaloacetate produced accumulates, measures on an average only 60% of the GOT activity of rat serum. 3. (3) Two isoenzymes of GOT from rat liver and serum were separated by agar gel electrophoresis, using a simple technique which gives a photographic record. 4. (4) The mitochondrial isoenzyme, GOT II, which predominates in the liver, appeared to be frequently absent from the serum of normal rats. It was just detectable in serum from two out of three rats with experimental liver necrosis. 5. (5) The soluble fraction isoenzyme, GOT I, was present in the serum of all the normal rats examined, and its zone of activity appeared much more intense following liver necrosis. Thus the increased serum GOT following liver damage is mainly in the form of GOT I. Possible explanations for this are discussed.