Intravaginal progestagens have been used for many years to synchronize estrus in ewes. This experiment compares two such treatments: 60 mg medroxyprogesterone (MAP) sponges and a controlled internal drug release (CIDR) device containing 366 mg natural progesterone. No pregnant mare serum gonadotropin (PMSG) was used. Treatments were given to groups of 10 to 20 ewes for 14 d at various times during breeding season. Rams were introduced 1 d after treatment removal, and day of mating was recorded. Rams were removed after 3 d. Pregnancy was checked with ultrasound 60 d later. There was no diffeence in rate of marking by rams (88%) or pregnancy rate (57%) between treatments. Ewes receiving CIDR devices showed estrus earlier and with closer synchrony (P < 0.01). The CIDR device is comparable to the MAP sponge for estrus synchrony during the breeding season, and reasonable fertility can be achieved without the use of PMSG.