Hormone Replacement Therapy in the Aged Female—Estrogen Bioassay.

Summary Estradiol benzoate (as a standard), alpha estradiol, estrone, and beta estradiol preparations were bioassayed using withdrawal bleeding from previously stimulated uteri of postmenopausal women as an assay end point. Alpha estradiol and estrone were equally effective in causing withdrawal bleeding, and each was about two-thirds as potent as estradiol benzoate. Beta estradiol was found to be altogether ineffective in a total dosage of 45 mg given over a 3 week period.