The synthesis of fatty acids and their esterification by blood from 12 cases of liver cirrhosis was studied in terms of incorporation of (14)C from 1-(14)C acetate into individual fatty acids in comparison with those found in the groups of 5 chemical diabetics, 5 overt diabetics, 6 cases of acute hepatitis, and 11 normal subjects. Of the patients of liver cirrhosis 6 cases were abnormal in glucose tolerance test (GTT) in spite of uncertain complication of primary diabetes and the rest was clinically considered to have been complicated with primary diabetes. The results were as follows. 1. It was proved in such major lipid classes as triglyceride (TG), Phospholipid (PL), and free fatty acids (FFA) that the depression of absolute distribution of the labelled fatty acids synthesized was found in every group of diseases as compared to normal controls, however in both TG and FFA fractions the most striking depression was found in the groups of liver cirrhosis with abnormal GTT, overt diabetics, and acute hepatitis. While the remarkable decrease in PL fraction was found in every group of liver diseases particularly in the groups of liver cirrhosis. 2. It was found in the diabetic groups that the percentage of synthesized fatty acids distributed to TG was lower and that distributed to PL was higher than normal group, on the contrary the percentage distributed to TG was higher and that distributed to PL was lower than normal group in both groups of liver cirrhosis. 3. Both groups of liver cirrhosis showed the striking increase of percentage distribution in 18:1 as compared to not only normal but diabetic groups and that this change was found in every fraction of TG, PL, and FFA. However the increase of the percentage distribution in 18:1 was most strikingly reflected to TG fraction, because the esterification of 18:1 was most specific for TG fraction and on the other hand the percentage of this fatty acid in the diabetic groups showed rather lower values as found in the normal group. In patients of liver cirrhosis the striking increase of the percentage distribution in 18:1 was weakened to some extent by complcating the primary diabetes in all lipid classes examined, nevertheless the pattern was rather analogous to that of liver cirrhosis than diabetics. The most part of 14:0 and 16:0 remained unesterified and the percentage distribution of these fatty acids in FFA or PL fraction was lower in the groups of liver cirrhosis and diabetics than that of normal controls or acute hepatitis. The esterification of fatty acids with retention time corresponding to 20:0 or longer was most specific for both TG and PL fractions and in these fractions the percentage distribution of these fatty acids increased in the diabetic groups and decreased on the contrary in the groups of liver diseases as compared to normal group. No particular differences were found among each group in the percentage of 16:1 and 18:0 in every lipid classes. 4. In acute hepatitis the fatty acid synthesis by blood showed some quantitative decrease, little qualitative changes in the percentage distribution of individual fatty acids were found in every lipid class as compared to normal group.