It is generally believed that the activity of the sebaceous glands depends to a large extent on the gonads. The pituitary also appears to be involved in the physiology of these glands (Ebling, Ebling & Skinner, 1969; Nikkari & Valavaara, 1969; Thody & Shuster, 1970). The relationship between the pituitary and the sebaceous glands may be exerted via growth hormone and prolactin for Ebling et al. (1969) have shown that these pituitary hormones facilitate the effect of testosterone on sebum secretion. This present study was carried out to see whether the pituitary influence on sebum secretion is also mediated through the thyroid and adrenal glands. The rate of sebum secretion was measured (Archibald & Shuster, 1969) in 12- to 15-week-old rats which had received one of the following treatments: castration, castration and adrenalectomy, castration and thyroidectomy, castration and hypophysectomy, or no treatment (intact controls). Castration was carried out when the