Metastin (kisspeptin-54), a member of the RF-amide family of peptide hormones was first described as a metastasis’ suppressor in melanomas. Kisspeptin peptides and their G-protein coupled receptor (gpr-54) were subsequently shown to be expressed in placenta, where they modulate trophoblast cell migration. More recently, a role for kisspeptins and gpr-54 in the hypothalamic arcuate nucleus, anteroventral periventricular nucleus and median eminence, regions of the brain involved in regulation of fertility, has been established. The kisspeptin system is a major regulator of reproduction via its stimulatory effects on the secretion of gonadotropin releasing hormone (GnRH). Antagonists of kisspeptin action may therefore be therapeutically useful in treatment of conditions affecting the reproductive system. We analysed structure-activity relationships of synthetic kisspeptin-10 analogues using a transfected CHO cell line stably expressing human gpr-54. Effects of analogues on binding of 125I-labelled kisspeptin-10 (YNWNSFGLRF-amide) and on stimulation of 3H-inositol phosphate production were assayed. Results showed that amino acid residues in the C-terminal section of kisspeptin-10 are important for binding to gpr-54, specifically: Phe6, Arg9 and Phe10. These residues may constitute a pharmacophore structure, since substitution with different residues reduced binding affinity. Further studies indicated that modification of these residues resulted in antagonism of inositol phosphate production. Since kisspeptins act upstream relative to GnRH, it is possible that kisspeptin analogues may be developed that are faster-acting and more effective than GnRH antagonists.