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The presence of a substance or substances possessing gonadotropic activity, presumably of pituitary origin, in the serum of ovariectomized women was first demonstrated by Fluhmann( 1 ) . Subsequently, Cohn and his collaborators ( 2 ) reported the detection of two gonadotropic hormones in fractions prepared from certain pools of human plasma. Since these findings could not be fully confirmed in later studies,t we have reexamined the distribution of pituitary gonadotropic activity among various plasma fractions. The bulk of the gonadotropic activity has been located in Fraction I1 + 111, and by subfractionation has been partially purified. Preliminary reports of these studies have appeared elsewhere (394) 9Methods and materials. Postmenopausal plasma was employed exclusively in this study, preliminary bioassays having shown that gonadotropic activity is readily demonstrable in the whole plasma of postmenopausal women, but not in that of men or of adult women of menstrual age. The donors were healthy women 65 years of age or less who were not undergoing treatment with estrogenic preparations of any kind.$ The blood was collected either with citrate or through cationic exchange resins in the ADL-Cohn blood fractionating machine. The data * This work was supported by grants from Barbara C. Willcox Fund of Vincent Memorial Hospital, Amer. Cancer SOC. (Mass. Division), and 'by research grant RG-4444 from National I.H., P.H.S. t Unpulblished data.$ Previous experience has shown that unwitting ingestion of estrogen occasionally results in significant contamination of plasma !pools. Therefore, the whole plasma and those fractions found to produce an increase in uterine weight of intact rats were assayed for estrogen in spayed rats by (modification of method of Bulbring and Burn(5). No indication of estrogenic activity was found. Harvard Medical Schoolherein reported were obtained by fractionating a 10-liter plasma pool which comprised the donations of 40 women, and are identical with the results previously obtained from the fractionation of 20 individual or pooled plasma samples from 3-12 donors. The cold ethanol method VI described by Cohn et al.(6) was employed for the initial plasma fractionation. The following fractions were prepared: Fraction I containing the fibrinogen; I1 + I11 consisting of P-lipoproteins and gamma globulin ; IV-1 containing the a-globulins and cholesterol; IV-4 consisting of Uand P-globulins and the metal-combining globulin; V, which contains the bulk of the albumin ; and VI, the supernatant remaining after fractionation. Partial purification of the gonadotropically-active material in Fraction I1 + I11 was accomplished by precipitating the bulk of the biologically-inactive proteins with zinc. Fraction I1 + I11 was brought to the original plasma volume with 0.15 M sodium chloride and zinc glycinate added until a 5 mM zinc concentration was obtained at a pH of 6.8 and a temperature of 0°C. The supernatant was freed of zinc by dialysis against ethylene diamine tetra-acetic acid (EDTA) and sodium citr...

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