The Bio-assay of β-Estradiol *

Occasionally, a scientist makes a discovery which stands out clearly as the contribution which has had a profound effect on the subsequent developments and advance in a particular field of science. That Edgar Allen's introduction of the vaginal smear method' for detection of the "ovarian follicular hormone" was such a discovery is evidenced by the tremendous advances in our knowledge of ovarian physiology and in the chemical study of the estrogens resulting from the application of his method. Allen's contribution was the base upon which many subsequent investigations in all parts of the world were founded. Although Allen's original procedure has been modified in many respects, still the basic principle remains unchanged. Nearly every investigator in the estrogen field has developed his own modifications of assay technic. In this laboratory five different procedures have been used for many years in the study of the activity of estrogens. This report deals in part with the potencies of P3-estradiol, P-estradiol3-benzoate, estrone, and a-estradiol as determined by these technics. P-Estradiiol was first obtained by Schwenk and Hildebrandt"5 by catalytic reduction of estrone. Subsequently, Butenandt and Goergens2 and Wintersteiner et al.'8 reported more details on its preparation, chemical and physical properties, and potency, and Wintersteiner and Hirschmann'7 reported its isolation from the urine of pregnant mares. More recently, Stroud,'6 Fish and Dorfman,8 Heard et al.,9 and Pearlman and Pearlman"3 have shown that P-estradiol is an important metabolite of a-estradiol and estrone in certain species of laboratory animals. Our interest in the metabolism of estrogens has led us (Doisy, Thayer, and Van Bruggen0) to a study of the products of excretion following the administration of P-estradiol to a monkey. An increase