Kisspeptin (KiSS) has been demonstrated to elicit LH and, in some cases, FSH release in several species. The proposed hierarchical role of KiSS stems from the ability of GnRH antagonists to mitigate a KiSS initiated pituitary release of LH and identification of KiSS immunoreactive neurons associated with GnRH neurons in hypothalamic nuclei considered key to reproductive neuroendocrinology. Elucidating the role of KiSS in a seasonal breeder such as the equine is not only important to reveal the underlying physiology of vernal transition, but could potentially impact a multi-million dollar industry. The objective of this study was to evaluate the change in peripheral FSH in diestrous mares (n=12) following three doses of rat KiSS decapeptide (1.0 µg, 0.5 mg, 1.0 mg KiSS-10, iv). To ensure pituitary responsiveness, a challenge of GnRH (250 µg, iv) was administered 4 h after treatment. Jugular blood samples were collected hourly from 2 h before to 4 h after treatment administration, and one hour after GnRH challenge. Serum concentrations of FSH were analyzed by RIA. Data were analyzed by ANOVA in a Latin Square design with repeated measures, such that each mare received each of the three treatments, allowing for a 48 h washout period between treatment days. KiSS-10 elicits (P < 0.05) a peak FSH response within one hour of treatment at doses of 0.5 mg (mean ± SEM, 185 ± 30 vs. 98 ± 9 ng/ml) and 1.0 mg (177 ± 41 vs. 97 ± 13 ng/ml), leading to almost a fold increase in serum FSH as compared to the pre-treatment period, respectively. However, the lowest dose of KiSS-10 (1.0 µg) did not lead to an increase in serum FSH as compared to the pre-treatment period (123 ± 18 vs. 120 ± 17 ng/ml). All mares were responsive to GnRH challenge (247 ± 25 ng/ml vs. 99 ± 8 ng/ml) and the magnitude of the serum FSH release following GnRH challenge was similar to that induced by 0.5 mg and 1.0 mg KiSS-10. The FSH data are consistent with our previous data demonstrating an increase in serum LH following peripheral KiSS-10 administration in the diestrous mare at the doses used in this study. Studies are currently underway to determine the potential effect of KiSS-10 on primary cultures of equine pituitary cells such that we may further our understanding of KiSSs role in the equine hypothalamic pituitary gonadal axis. This research was generously supported by the American Quarter Horse Foundation and the Preservation for Equine Genetics Foundation at Colorado State University.