The estrus-inducing hormone was prepared in the form of a gelatin pessary for vaginal administration. The check of potency of the gelatin pessaries by injection of water emulsion of these pessaries in white rats showed that no loss in potency occurred in their preparation. The estrous cycle has been induced in spayed albino rats by vaginal administration of the follicular hormone. The ratio between the pessary dose and the subcutaneous dose is probably in the neighborhood of 3 to 1. Menstruation has been induced in spayed monkeys by the vaginal administration of these pessaries. As low as 150 units will induce menstruation in these animals.