The aim of this study was to evaluate the changes in fatty acid composition of lipids of plasma, erythrocytes, and liver microsomes in rats with liver cirrhosis induced by oral intake of thioacetamide and to determine to what extent the experimental model reproduces the fatty acid tissue alterations reported in human cirrhosis. Two groups of rats were studied. The control group received water ad libitum, and the experimental group received 0.03% w/v thioacetamide in drinking water for 2, 4, and 6 months. At these times, lipids of plasma, erythrocytes, and liver microsomes were extracted, and their fatty acid compositions were determined. Thioacetamide intake led to macronodular and micronodular cirrhosis at 2 months. These alterations progressed at 4 months and eventuated in liver tumors at 6 months. Thioacetamidetreated rats showed a drop in total plasma fatty acids, higher percentages of palmitic acid in all lipid fractions, and lower levels of stearic acid in erythrocyte lipids and liver microsomal phospholipids. Oleic acid increased in plasma cholesteryl esters and phospholipids, as well as in erythrocyte lipids and liver microsomal phospholipids. In plasma lipids and liver microsomal phospholipids, the percentages of arachidonic and docosahexaenoic acids decreased. The latter also decreased in erythrocyte lipids. In addition, liver microsomes showed a higher cholesterol/lipid phosphorus molar ratio. The experimental model of cirrhosis obtained by intake of thioacetamide in drinking water for 4 months reproduces many of the fatty acid tissue alterations that appear in human cirrhosis and may serve to ascertain the biochemical mechanisms involved in these changes. (Hepatology 1995;21:199–206).