CONTEXT: Kisspeptins stimulate GnRH and thus gonadotropin secretion. Kisspeptin-10 is the minimal kisspeptin sequence with full intrinsic bioactivity, but it has not been studied in man. OBJECTIVE: We investigated our hypothesis that kisspeptin-10 increases GnRH and thus LH pulse frequency. DESIGN AND PARTICIPANTS: The dose response of kisspeptin-10 was investigated by administering iv bolus doses (0.01–3.0 µg/kg) and vehicle to healthy men. Effects on LH pulse frequency and size were determined by deconvolution analysis during infusion of kisspeptin-10 for up to 22.5 h. RESULTS: Intravenous bolus kisspeptin-10 resulted in a rapid and dose-dependent rise in serum LH concentration, with maximal stimulation at 1 µg/kg (4.1 0.4 to 12.4 1.7 IU/liter at 30 min, P < 0.001, n=6). Administration of 3 µg/kg elicited a reduced response vs. 1 µg/kg (P <0.05). Infusion of kisspeptin-10 at 4 µg/kg h for 22.5 h elicited an increase in LH from a mean of 5.4 0.7 to 20.8 4.9 IU/liter (n=4; P <0.05)andserumtestosterone increasedfrom16.6 2.4 to 24.0 2.5 nmol/liter (P < 0.001). LH pulses were obscured at this high rate of secretion, but a lower dose infusion of kisspeptin-10 (1.5 µg/kg h) increased mean LH from 5.2 0.8 to 14.1 1.7 IU/liter (n=4; P <0.01) and increased LH pulse frequency from 0.7 0.1 to 1.0 0.2 pulses/h (P <0.05) and secretory burst mass from 3.9 0.4 to 12.8 2.6 IU/liter (P <0.05). CONCLUSIONS: Kisspeptin-10 boluses potently evoke LH secretion in men, and continuous infusion increases testosterone, LH pulse frequency, and pulse size. Kisspeptin analogues have therapeutic potential as regulators of LH and thus testosterone secretion.