Estrone sulfate levels were measured in the plasma of 63 postmenopausal women. The assay method involved prior extraction of the free estrogens, enzyme hydrolysis of the estrone sulfate with sulfatase and radioimmunoassay of the estrone liberated. The plasma levels ranged from 37 to 320 pg/ml (expressed as free estrone) with a mean value of 178 +/- 79 pg/ml. As observed in premenopause, estrone sulfate is quantitatively the most important circulating estrogen in postmenopausal women.
