The G protein-coupled receptor GPR54 (also designated KISS1R) is activated by cleavage products of the KiSS1 protein, the kisspeptins (KP), to act as a molecular switch for puberty. Additionally, KP are potent inhibitors of tumor metastasis and play a role in placentation, both processes involving angiogenesis. Our aim was to investigate if GPR54 and KP are expressed within normal and diseased human vasculature and what their functional role may be. RT-PCR screening of human blood vessels revealed a discrete localization of GPR54 mRNA in smooth muscle of vessels with the same developmental origins, aorta, coronary artery and umbilical vein, a pattern confirmed by immunocytochemistry and radioligand binding. Novel ligand [¹²⁵I]KP-13 exhibited saturable and high affinity binding in aorta smooth muscle sections (K_D 0.2 ± 0.03 nmol/liter), and using confocal microscopy, we found co-localization of receptor and peptide to vascular endothelial cells and to the atherosclerotic plaque of coronary artery. RIA detected 13.04 ± 2.94 and 20.50 ± 5.00 fmol/g KP in human coronary artery and aorta respectively. KP-10, KP-13 and KP-54 acted as vasoconstrictors with comparable potency and efficacy in isolated rings of coronary artery (pD₂, E_max: KP-10 7.89 ± 0.24, 33.7 ± 17.0; KP-13 8.66 ± 0.88, 35.1 ± 7.9; KP-54 8.86 ± 1.11, 25.7 ± 5.5) and umbilical vein (pD₂, E_max: KP-10 8.44 ± 022, 24.3 ± 3.7; KP-13 8.43 ± 0.88, 28.4 ± 8.6; KP-54 8.93 ± 0.39, 36.9 ± 5.2). In conclusion we have detected expression of both peptide and receptor in aorta, coronary artery and umbilical vein and have shown, for the first time that the KP are vasoconstrictors in human, suggesting a previously undescribed role for GPR54 and KP in the cardiovascular system.