1. 1. It has been shown that certain pathologic manifestations are correlated with sensitivity toward endogenous hormones. They have been designated, therefore, as conditions of “endocrine allergy.” 2. 2. In certain pathologic conditions, related to the menstrual cycle or the appearance of menopause, skin reagins to the steroid hormones—estrone, estrone, estradiol, progesterone, pregnandiol, testosterone, androsterone, or desoxycorticosterone acetate—can be demonstrated in the patient by active cutaneous tests. Analogous conditions of sensitivity to insulin and prolan may occur. 3. 3. Allergic endocrine hypersensitiveness may also be demonstrated by the “recurrent test,” i.e., by the appearance of a local reaction at the site of a first intracutaneous test, following a subcutaneous injection twenty-four hours later of the allergenic hormone at a new site. 4. 4. When the cutaneous reaction in cases of endocrine allergy is delayed, it often occurs in the premenstruum, viz., at a time coincident with the attainment of maximum level in the body by the allergenic hormone in question (“retarded test reaction”). 5. 5. Normal subjects injected intracutaneously with serum of patients hypersensitive to estrone yielded positive cutaneous reactions when a solution of estrone was given subsequently at the site of the former serum injection (positive Prausnitz-Kuestner test). Serum of patients hypersensitive to estrone may also cause positive cutaneous reactions following its intracutaneous injection into normal subjects; this occurs when the concentration of hormonal allergen in the body of the normal subject reaches high values (either physiologically or following injection). 6. 6. The properties of reagins induced by hormonal allergens have been identified as similar to those of allergic reagins in general. 7. 7. The degree of specific reactivity of the skin, to hormonal allergens injected intracutaneously, is related to the amount of the active principle in the solution tested. 8. 8. Injections of minimal quantities of steroid hormones in oily vehicle, into persons who have not previously received hormone treatment, may cause serious general symptoms. 9. 9. Personal and family histories of allergy and high blood eosinophilia are frequent in persons with positive cutaneous tests. 10. 10. Favorable clinical results, obtained by desensitization, furnish a further proof that the disturbances in question are caused by endocrine allergy. 11. 11. Allergy to endogenous hormones has been observed in women suffering from disorders related to menstruation or menopause, but never in healthy subjects. 12. 12. The results of our investigations lead us to assume that certain gynecologic conditions like pruritus vulvae, and various premenstrual disorders are conditioned by allergy to endogenous hormones. This is also true for disturbances, known to be of allergic nature (asthma, vasomotor rhinitis, angioneurotic edema, and urticaria) related to menstruation or menopause.