Binding and internalization of rat low density lipoproteins (LDL) by fetal rat liver cells were studied under in vivo and in vitro conditions by ultrastructural and biochemical methods. By using LDL-gold conjugates it could be shown that on day 22 of gestation hepatocytes and Kupffer cells mainly contribute to specific binding and uptake of LDL, but not endothelial cells. Estrogen administration to the pregnant rats stimulated binding and internalization of LDL-gold. The binding characteristics of isolated fetal hepatocytes were determined by 125I-LDL. The data allow the conclusion that fetal hepatocytes and Kupffer cells possess specific B/E receptors.