The estrogen and progesterone receptor content of liver cytosol was measured in female patients with focal nodular hyperplasia associated with oral contraceptive use and compared with the receptor content of non-tumorous liver and of primary hepatocellular carcinomas. Receptors were found in very low concentrations or were not measurable at all. In one case of focal nodular hyperplasia the estrogen receptor content of the tumor was higher than that in the adjacent normal liver. Malignant liver tumors and the male liver were characterized by a low or non-measurable receptor content. The study of nuclear receptors combined with the use of monoclonal antibodies may be more helpful in elucidating the complex relationship between oral contraceptive use, benign liver tumors and hepatic steroid receptors.