Abstract
Recent progress in bioassay and biochemical assay has made it possible to detect the small amount of blood progesterone, which could not be caught before by Corner-Allen (1929) and Clauberg (1930) assay. As for the blood progesterone level during the human menstrual cycles several investigators attempted to determine and reported not so different results, namely they estimated that the blood plasma contained 4 to 10mcg per cubic centimeter as maximal concentration in the luteal stage. However , during the pregnancy which can be regarded as a prolonged luteal stage at least in the first trimester, they could curiously detect no or only small amount of progesterone in the blood. This discrepancy seems to be diffcult
to explain. In the present paper it was attempted to re-examine the systemic plasma levels of free progesterone during the human !,gestation period
by means of the intrauterine stromal nuclear assay developed by Hooker & Forbes (1947).
