A comparative study has been made of the accumulation and synthesis of cholesteryl esters in the liver, yolk sac membrane, and yolk contents of the chick embryo during the last week of development. This involved a comparison of the cholesteryl esters synthesized during incubation in vitro with 14C-cholesterol with those accumulated during incubation in vivo. Results indicated that the considerable accumulation of cholesteryl esters, mainly cholesteryl oleate, that occurred within the liver during embryo development arose from synthesis in the yolk sac membrane. This suggested a specific role in the transport of yolk lipid into the embryo. With the approach of hatching the ability of the liver to synthesize its own cholesteryl esters increased while that of the yolk sac membrane decreased.