The cytosol extracted from a vascular endothelial cell line binds [3H]estradiol with high affinity and a high degree of specificity. In contrast, in experiments performed with cytosol labeled in the intact cell, progesterone and, to a smaller extent, testosterone gave an apparent inhibition of estradiol binding. These data support the concept that ovarian hormones may influence the role of the endothelium in various physiological and pathophysiological conditions.