When the ovary of a laying hen contains a mature follicle, ovulation can be induced by an injection of corticosterone. The dose which is required to consistently induce a premature ovulation causes the plasma concentration of corticosterone in the peripheral blood to rise to levels which are higher than those normally observed during the ovulation cycle. The accompanying rise and fall in progesterone which follows an injection of corticosterone. It was concluded that the pituitary gland for both ovulation and progesterone secretion to occur.