Kisspeptin signaling is a potent regulator of the reproductive axis and an elicitor of gonadotropin-releasing hormone secretion. The present study assessed the effect of the peripheral administration of a kisspeptin antagonist (P234) on testosterone secretion in the adult male rhesus monkey. Five monkeys were administered with either P234 (38.8 µg/kg body weight) or a vehicle (0.9% saline). Plasma testosterone and adiponectin levels, as a positive control, were then measured using specific ELISA assays from blood samples collected sequentially at 15-min intervals from 60 min prior to until 360 min after the P234/vehicle injection. In 3 monkeys, the experiment was repeated where the animals received a kisspeptin-10 (50 µg) challenge 30 min after the P234 or vehicle treatment. No effects on basal testosterone levels were found after the systemic administration of P234. Plasma adiponectin levels were found to be briefly decreased by P234. P234 administration was found to suppress kisspeptin-dependent testosterone release and to inhibit kisspeptin-dependent adiponectin release. This suggested that the systemic administration of P234 was effective peripherally. However, the minimal peripheral effects on testosterone secretion in the male macaque suggested that P234 did not cross the blood-brain barrier and blocked the peripheral kisspeptin receptors.