Perfluorodecanoic acid (PFDA) is a peroxisome proliferator that causes a dose-dependent (20-80 mg/kg) increase in hepatic triacylglycerol and cholesteryl ester levels in the rat. We hypothesized that PFDA may cause an increase in the de novo synthesis of fatty acids and cholesterol in this species, which would explain observed effects. The incorporation of 3H2O into tissue lipids was examined 7 days after rats received vehicle or 20 or 80 mg/kg of PFDA. PFDA treatment decreased the rate of synthesis of cholesterol and fatty acids in the live and in epididymal fat pad. At a PFDA dose (20 mg/kg) that decreased de novo synthesis of fatty acids and cholesterol, there was no effect on the concentration of fatty acids and cholesterol in the liver, epididymal fat pads, and plasma. We conclude that PFDA induced fatty liver is due to either a decrease in the oxidation of fatty acids in the liver, or an impairment of triacylglycerol catabolism and/or export from the liver, and is not the result of an increase in de novo synthesis of fatty acids and cholesterol.