Kisspeptin-54 is a peptide ligand of the orphan G protein-coupled receptor GPR54 (Kis = 1.81 and 1.45 nM for rat and human receptors, respectively).1 It is a 54 amino acid peptide encoded by the metastasis suppressor gene KISS-1. Kisspeptin-54 induces calcium mobilization in CHO-K1 cells expressing rat and human receptors (EC50s = 1.39 and 5.47 nM, respectively). It also induces arachidonic acid release in CHO cells expressing rat and human GPR54 in a concentration-dependent manner. Kisspeptin-54 (10-1,000 nM) inhibits insulin secretion from isolated mouse pancreatic β-cells in the presence of 2.8 mM, but not 11.1 mM, glucose.2 Kisspeptin-54 (1-5 nmol, i.c.v.) increases serum levels of luteinizing hormone (LH) and follicular stimulating hormone (FSH) in mice, an effect which is reversed by the gonadotropin releasing hormone (GNRH) antagonist acycline.3