Estrone (E1), a principal estrogen in postmenopausal women, may have profound consequences in the maintenance and progression of hormone-sensitive endometrial carcinoma. This study was designed to investigate the specific binding sites for E1 in the tumor and in the normal endometrium. The binding of [3H]E1 to the cytosolic fraction and KCl-soluble nuclear fraction from 3 endometrial carcinomas showed saturation kinetics with an apparent equilibrium dissociation constant of approximately 37 and 50 nM, respectively. The specific binding site of E1 was also found in 3 normal endometria. However, the binding capacity in the endometrial carcinoma increased to 1.5-fold of that in the normal endometrium. E2 did not affect [3H]E1 binding to any sub-cellular fraction from endometrial carcinoma specimens. These findings demonstrate the presence of specific binding sites for E1 in human endometrial carcinoma. The endometrial carcinoma growth may be mediated, at least in part, by E1 and its binding site interaction.