Summary Sixty mares determined to be in late transitional phase were used to examine the effectiveness of short term progestin and human chorionic gonadotropin (hCG) in hastening onset of the breeding season. A second group of thirty mares was used to examine the effectiveness of hCG alone. Altrenogest, 22 mg administered orally daily for 7 days, was not effective (p>0.10) in reducing interval to ovulation or duration of estrus. Irrespective of prior altrenogest therapy, hCG (3,300 IU), when administered intravenously in these same mares, reduced (p 0.10) interval from treatment to ovulation, but caused more (p 0.05) in hastening onset of the breeding season.