The present study was conducted with the aim to elucidate the mechanism of transaminase release into blood from damaged liver cells. Observations were made on the fluctuations of the transaminase activity in various cell fractions of the liver as well as on the changes of serum GOT-isozyme patterns in various diseases through quantitative analysis by means of starch electrophoresis. In the rats with acute liver injury there were increases of GOT and GPT activities in blood on one band and contrarily decreases of these in the liver cells on the other. The changes of the mitochondrial GOT and GPT activities, as judged from the decreasing rate, fairly parallel with those in the supernatant fraction. In the electrophoretic assay of serum GOT in these cases the elevations of the serum GOT activity is assumed to be most likely due to that in the supernatant fraction, but about 10% of the serum GOT can be considered to be released from the mitochondrial fraction at the stage that clearly showed necrosis under light microscpe. In the electrophoretic analysis of serum GOT obtained from patients with various liver diseases it has been observed that of the 10 cases of acute hepatitis showed an increase of the supernatant GOT with appearance of the mitochondrical GOT. In contrast liver cirrhosis showed no apperance of mitochondrial GOT.