Unoccupied estrogen receptors and progesterone receptors were measured in the cytoplasm of five sections along the length of endometrium obtained from noncancerous, premenopausal hysterectomy specimens. The concentrations of the two receptors were measured with tritiated estradiol or R5020 (a synthetic progestin), the latter two having been purified by high-pressure liquid chromatography, and were found to be highest in the fundus and lowest in the cervix. Progesterone receptor levels, ranging from 50 to 3,500 fmoles of R5020 bound per milligram of protein, were generally much higher in each section of the endometrium than estrogen receptor levels, which ranged from 0 to 500 fmoles of estradiol bound per milligram of protein. Near ovulation it seemed that the distribution profiles of both receptors became very steep, with more than a tenfold difference in the receptor levels being found between the fundus and the cervix. Receptor levels measured in endometrial samples obtained by curettage or aspiration should be interpreted with caution.