The present study was conducted to quantify in vitro GnRH release parameters in the male marmoset, and compare it with that of the well established male rat model. We established primary cultures of rat and marmoset hypothalamic tissues for ~2 days (marmosets) or ~3 days (rats) to assess GnRH release profiles in vitro in hypothalamic explants from testis-intact and gonadectomized males. Pulsatile GnRH release profiles were readily demonstrated from in vitro hypothalamic explants isolated from adult male marmoset monkeys and male rats. Male rats showed no changes in any concentration or frequency release parameters for GnRH following gonadectomy or during successive days in culture. In contrast to rats, gonadectomy of male marmosets resulted in elevated mean GnRH and pulse amplitude from hypothalamic explants on the first day of culture (Day 0). In testis-intact marmosets, GnRH pulse amplitude increased by day 2 in ~67% of hypothalamic explants, suggesting release from an endogenous regulator of GnRH, such as testosterone. The present study represents a unique examination of GnRH release from male marmoset monkey hypothalamic tissue, and compares release dynamics directly with those obtained from male rat suggesting a species difference in feedback regulation of GnRH release.