The present study has been conducted by gaschromatography to determine the compositions of total plasma fatty acid in liver diseases. The subjects studied comprised 73 cases of various liver diseases, 10 cases of diabetes mellitus and 10 normal persons. The results obtained by this study are summarized as follows: 1. The compositions of total plasma fatty acid in the cases with jaundice were almost similar to those without jaundice; namely, an increase in palmitate, palmitoleate and oleate, and a decrease in linoleate. 2. The level of palmitoleate increased remarkably in all liver diseases, although it remained unchanged in diabetes mellitus. It is interest that an increased level of palmitoleate related to the extent of liver injuries, such as acute stadium of acute hepatitis> obstructive jaundice> active form of chronic hepatitis> fatty liver> convalescent stadium of acute hepatitis> inactive form of chronic hepatitis> Gilbert's disease. The increases in the palmitoleate was found in liver cirrhosis in order of cases with normal Glucose Tolerance Test (GTT), those showing abnormal GTT and those comlicated with primary diabetes. In contrast with cirrhosis, palmitoleate levels in active form of chronic hepatitis without diabetes mellitus could not be distinguishable from that with diabetes mellitus. Liver diseases as well as severe diabetes mellitus showed an increase in palmitate and oleate and a decrease in linoleate and L/O ratio. The decreased levels of arachidonate in acute hepatitis, and their increases in chronic hepatitis and fatty liver appeared to be characteristic. No change was found, however, in mild diabetes mellitus. 3. The increased levels of palmitoleate was found in the acute hepatitis of which liver function was normalized, but still remained abnormally high even when liver function test became complitely normal. However, some acute hepatitis showing abnormal liver function test and most of chronic hepatitis always showed abnormally high level of palmitoleate through the courses. In the biliary cirrhosis due to choledocus carcinoma, palmitoleate increased remarkably as the liver function grew worse. 4. Palmitate and linoleate had the positive and negative correlation, respectively, to serum total lipid in the cases without jaundice. 5. The high concentration of total lipid in serum was observed in acute hepatitis, obstructive jaundice, liver cirrhosis complicated with primary diabetes and sever diabetes. 6. Cholestyramine was given in 4 cases of jaundice, but no change in the compositions of total plasma fatty acid occurred. 7. Any detectable alteration in both the fatty acid synthesis and its oxidation using liver tissues obtained by needle biopsy from 7 cases without jaundice was not found.