Desaturation of fatty acids is thought to facilitate their incorporation into glyceride and their subsequent secretion as lipoproteins. However, in the laying hen, the dramatic increase in hepatic lipogenesis is often paralleled by a liver steatosis that may affect egg production and even result in death. The balance between lipid secretion and storage, in relation to the fatty acid desaturation process, was therefore investigated in young male estrogenized chicken. Estrogen stimulation resulted in a dramatic increase in VLDL concentration (40.4 mg/ml versus 0.158 mg/ml in control) and hepatic lipid content (8.61 g/liver versus 1.47 g/liver in control). In estrogenized chickens, VLDL, total liver, and microsomes contained relatively more monounsaturated and less saturated and polyunsaturated fatty acids, whereas hepatic delta 9 desaturase activity was twofold higher. Moreover, in these birds, the proportion of monoenoic fatty acids was greater in VLDL (55%) than in the liver (50%), which was indicative of their preferential secretion. Therefore, under the influence of estrogen, fatty acid synthesis and desaturation are associated with and increased VLDL secretion, which limits the degree of hepatic accumulation of triglyceride and the risk of subsequent steatosis.