In the blood of 39 women with endometrial carcinoma the FSH, LH, estrone, androstendion, estradiol and dehydroepiandrosterone were determined by the RIA method. Compared to the control group the estrone (303.3 +/- 44.3 pmol/l), estradiol (165.2 +/- 29.4 pmol/l) and the androstendion (5.24 +/- 0.44 nmol/l) were significantly higher. The source of the increased estrogen levels was mainly of adrenal origin. The peripheral conversion, i.e. aromatization of androstendion into estrone was particularly marked in the case of adipose patients. The unbalanced estrogen effect in the absence of progesterone is one of the decisive factors in the etiology of endometrial carcinoma.