Previous experiments have shown lower abdominal and body fat deposition in broilers fed polyunsaturated fatty acids (PUFA) compared with those fed saturated fatty acids (SFA) or monounsaturated fatty acids (MUFA). These changes in fat deposition may be related to different rates of lipid synthesis or lipid oxidation. In Experiment 1, in vivo lipogenesis of broilers fed different dietary fatty acid profiles (tallow, sunflower oil, or linseed oil) was investigated. In Experiment 2, liver fatty acid deposition of broilers fed a basal diet (without additional fat) or diets with added tallow, olive oil, sunflower oil, or linseed oil was studied. Results from Experiment 1 showed higher rates of de novo fatty acid synthesis in broilers fed the diet with added linseed oil (P < 0.05), compared with those fed tallow or sunflower oil. In Experiment 2, values of liver-to-dietary-fatty-acid ratios of fatty acids from endogenous synthesis (SFA, n-7 and n-9 fatty acids) were higher in broilers fed linseed oil and the basal diet. Results obtained in both experiments suggest that lower abdominal and body fat deposition of broilers fed PUFA compared with those fed SFA or monounsaturated fatty acids is mainly due to differences in lipid oxidation rates and that the higher in vivo lipogenesis found in broilers fed linseed oil would be another mechanism to dissipate energy, contributing to the lower fat deposition in these birds.