The content of hepatic phospholipids, cholesterol and triglycerides was studied in 14, 17 and 20 day old chick embryos and newborn chicks (21 incubation days). An increase in the total lipid content and in the other lipidic fractions throughout embryo development is observed, mainly between 17 and 20 days of incubation, remaining practically constant until the hatchability day. Nevertheless a sharp depletion of triglycerides in broken eggshell day is revealed. Effect of a single dose of 3-3'-5-Triiodothyronine (T3) on hepatic lipid levels was determined. Throughout embryonary period, the hormone only affects triglyceride levels enhancing its biosynthesis in the 20th incubation day. All the other variations are described in newborn animals.