The present experiments were carried out on the relationship between triglyceride synthesis and fatty acid oxidation in liver of chicks treated by estrogen, in order to study on the mechanism underlying estrogen-induced hypertriglyceridemia. Estrogen treatment increased the incorporation of 14C-acetate into fatty acid and of 14C-palmitate into triglyceride in vivo and in vitro. This result suggests that triglyceride synthesis is stimulated by estrogen.The 14C incorporation from [1-14C] palmitate into CO2 in vivo and in vitro was decreased by estrogen treatment, whereas that from [1-14C] acetate into CO2 in vitro was increased.This result suggests that fatty acid oxidation is suppressed by estrogen.The results described above suggest that the combination of increased rate of triglyceride synthesis and decreased rate of fatty acid oxidation in liver may, at least in part, contribute to estrogen-induced hypertriglyceridemia. The specific activities of all the hepatic lipogenic enzymes examined were increased by estrogen treatment.Jpm. J. Zootech. Sci., 53 (10): [699][700][701][702][703][704][705][706] 1982