Human Chorionic Gonadotropin (HCG) is major physiological luteotropic factors for the human corpus luteum. The observations strongly suggest that the human ovary possesses a gonadotropin receptor in the cell membrane. We studied the HCG receptor in normal human ovary and ovarian tumors. Twenty-three human ovarian specimens and 16 ovarian tumor specimens were obtained from women patients having gynecological surgery. Ovaries were homogenized and sonicated. The homogenates were centrifuged at 2000 g for 15 min. After sucrose density gradient ultracentrifugation (78,000 g, 4 h), two fractions were collected from layer of 33% and interface between 33% and 37%. Thirty micrograms of ovarian protein, 8 ng 125I-HCG and unlabeled HCG in a final volume of 0.5 ml of 0.05 mol/L Tris buffer were incubated at 30 degrees C for 2 h. The results were shown in the table.