A study was carried out to shed light on the mode of action and the quantitative interrelationships between the levels of 17 beta-estradiol and progesterone in the blood plasma, colostrum, and amniotic fluid. The idea was to elucidate more fully the question on the role played by colostrum as a stimulant with regard to the polycyclic functions in farm animals. The evaluation of both agents was performed with the aid of KIT (IRC Sorin Torino). Radioimmunologic results showed that there was positive correlation with the levels of 17 beta-estradiol in the plasma, colostrum, and amniotic fluid of cows that spontaneously rejected their placenta up to the second hour after calving.