Sheep are seasonal breeders, experiencing a period of reproductive quiescence during spring and early summer. During the non-breeding period, kisspeptin expression in the arcuate nucleus is markedly reduced. This strongly suggests that the mechanisms that control seasonal changes in reproductive function involve kisspeptin neurons. Kisspeptin cells appear to regulate GnRH neurons and transmit sex-steroid feedback to the reproductive axis. Since the non-breeding season is characterized by increased negative feedback of estrogen on GnRH secretion, the kisspeptin neurons seem to be fundamentally involved in the determination of breeding state. The reduction in kisspeptin neuronal function during the non-breeding season can be corrected by infusion of kisspeptin, which causes ovulation in seasonally acyclic females.