Secretion of LH, as measured by ovarian ascorbic acid depletion in mature female rats with luteinized ovaries, is induced by pitressin and adrenaline. Other drugs (pitocin, histamine, acetylcholine, serotonin, salycilate, insulin) and stress procedures (formalin, ether anaesthesia, unilateral and total adrenalectomy, laparatomy, asphyxia and electric shock) are without effect in this test. No LH activity is detectable by the ovarian ascorbic acid method in 0.5 ml of serum of normal female rats; LH becomes detectable in 0.5 ml of serum 2 weeks after castration; high titers of blood LH are observed in female animals which have been castrated for more than 12 months. No LH is present in the blood of female castrated rats treated with progesterone.