A concentration of pregnancy-related transcortin variety was detected in the venous blood serum of women at varying time of normal pregnancy and after delivery as well as in umbilical and retroplacental blood serum using a radio-immunoassay. This transcortin variety was found in the blood at early stages of pregnancy (the end of the 1st-the start of the 2nd trimester). During pregnancy the content of this variety increased, mainly in the 2nd trimester. At the end of pregnancy transcortin variety concentration achieved values typical of retroplacental blood serum, corresponding to approximately 10% of total transcortin concentration. The absence of transcortin variety in the umbilical blood serum and a slight decrease in its level in the mother's blood by the 5th day after delivery can be suggestive of the fact that this protein is synthesized in the mother's body and does not penetrate the placental barrier.