In biochemical studies it was found that the binding capacity of cytoplasmatic estrogen and progesterone receptors in the uterine cervix undergo characteristic changes during the menstrual cycle. The highest estrogen binding values were observed by the eighth day, after which there was a significant drop. The highest progesterone binding values were around the twelfth day, followed by a significant drop after ovulation. In sexually mature subjects the estrogen receptors predominated in the mucosa and the progesterone receptors in the myometrium. Therefore, there is obviously a parallel to the receptor content in the corpus uteri. The maximum estrogen and progesterone binding capacities were in each case ascertained some days before the maximum E2 and Pr values were attained in the serum. Hence, the estrogen receptors have already built up in the uterine cervix before optimal functional activity, measured by the cervix score, has been attained. Anti-estrogens given at the beginning of the cycle can disturb this sequence. The high estrogen receptor content in the endometrium at the beginning of the cycle creates the necessary conditions for the explosive, proliferative gland growth around this time, even though the serum estrogen concentration is still relatively low. In the postmenopause the estrogen binding capacity in the uterine cervix was higher than during sexual maturity, while the reverse was the case with the progesterone binding capacity.