Groups of twelve 21-day-old rats receiving large doses of yohimbine, cantharidin, and histamine, and 3 rabbits receiving yohimbine and cantharidin, showed marked hyperemia of the genital organs, but no ripe follicles or changes in the vagina and uterus comparable to the condition produced by the injection of pregnancy urine. Cantharidin and yohimbine did not produce estrus smears in ovariectomized rats.