The discovery by Dodds, Golberg, Lawson, and Robinson [1938] of a new synthetic oestrogenic substance, diethylstilboestrol, with an oestrogenic potency resembling that of oestrone [Dodds, Lawson, and Noble, 1938; Freud, 1939] has stimulated investigations dealing with the further biological properties of this compound. The action of diethylstilboestrol proves to be similar in many respects to that of oestrone. This applies to its effect on the uterine mucosa [de Fremery and Geerling, 1939], the hypophysis [Noble, 1938], the male genital system [Gaarenstroom, 1939 b], the feathering of cocks and the comb of the capon [Mühlbock, 1939], the sex of the chick embryo [Gaarenstroom, 1939 a], &c. The synthesis of diethylstilboestrol is comparatively cheap and therefore this compound arouses clinical interest. With regard to its clinical application it was necessary to have exact information about a possible toxic action, since Loeser [1939] and Cobet, Ratschow, and Stehner [1939] recently reported toxic effects