That the sebaceous glands are affected by the sex hormones has been suggested by the clinical observations of Hamilton [1941], who observed the appearance of acne after administering androgens to human beings. Lawrence & Werthessen [1942] have reported successful treatment of this condition with orally administered oestrogens. Experimental work carried out by Hooker & Pfeiffer [1943] and De Graaf [1942, 1943] is referred to in the discussion. The object of this work was to devise a technique for the exact study of the effect of various hormones on the sebaceous glands of the rat. METHODS Groups of female Wistar rats having initial body weights of about 40–60 g. were injected subcutaneously with 1 or 100 μg. of oestradiol benzoate (Dimenformon), with testosterone propionate (Neo-Hombreol), or with 1/10 or 1/2 mg. of progesterone, each daily for about 30 days. The rats were killed, and the skins were removed from mid-dorsal incisions,