Biosynthesis of ceruloplasmin, a copper-containing glycoprotein, which plays an important role in copper transfer and bidirectional iron transport in vertebrates, was studied in 7-day old rats characterized by the embryonic type of copper metabolism. In addition to the liver, copper is synthesized in the lungs, brain, and kidneys. The appearance of labeled ceruloplasmin in the blood flow coincides with the time of liberation of de novo synthesized ceruloplasmin from the liver. [14C]-Ceruloplasmin is absorbed from the blood flow by cells of the heart, lung, and kidneys and binds to erythrocytes. The polypeptide ceruloplasmin chain does not enter the brain cells from the blood flow. Immunoreactive polypeptides of the ceruloplasmin receptor were found using immunoblotting in plasma membranes of the heart, liver, kidneys, and erythrocytes, rather than in those of the brain. It was shown by reverse transcription coupled with PCR using selective primers these cells contain molecular forms of ceruloplasmin mRNAs programming the synthesis of both secretory ceruloplasmin and ceruloplasmin connected with the plasma membrane via the glycosyl phosphatidylinositol anchor. After transition to the adult type of copper metabolism, the blood serum contents of copper and ceruloplasmin sharply increase, while the content of CP in the cerebrospinal fluid, as measured according to the oxidase and antigen activities, and copper concentration, as determined by atom-absorption spectrometry, remain low. Ontogenetic features of the system ensuring the copper homeostasis in mammals are discussed.