Three groups of ovariectomized rats were treated for 6 days: 1) estradiol benzoate (100 micrograms/kg) (SC) and fed ad lib; 2) vehicle-injected controls fed the same amount of food as eaten by estradiol-treated rats; 3) vehicle-injected, free-feeding controls. Specific binding of insulin to liver and hypothalamus slices was measured by quantitative film autoradiography. Estradiol-treated rats lost weight (p < 0.001) and had elevated plasma insulin (p < 0.01). Liver insulin binding in rats with estradiol treatment was greater (p < 0.01) than in rats without estradiol, but was less (p < 0.05) than in controls fed the same food levels as consumed by the estradiol-treated rats. Therefore, with equal food intake, estradiol decreased liver insulin binding. Insulin binding in the dorsomedial, ventromedial, and arcuate nuclei of the hypothalamus was unchanged by food intake or estradiol, however. Thus, altered insulin binding in the arcuate, ventromedial, or dorsomedial nuclei of the hypothalamus is probably not involved in the effects of insulin or estradiol on food intake.