Abstract
Cyclic ovulation and corpus-luteum formation were restored temporarily in persistent-estrus rats by crystalline proges- terone, injected in quantities between 0.2 mg. and 1.0 mg per day. 23 animals responded uniformly by showing a diestrous smear within 48 hrs. after the 1st inj. When the period of treatment was continued to include the following proestrus, an ovulatory cycle resulted. 13 of the animals were given progesterone in these small amts. over a long period, up to 55 days. As many as 10 consecutive cycles were obtained in this way. Withdrawal of the hormone was accompanied by prompt recurrence of persistent estrus.