A novel peptide found as gonadotropin-releasing hormone (GnRH) in octopuses, a member of mollusks. The structure and the activities of the peptide have been unraveled. The peptide finds use as a reagent used in the studies of correlations between the structure and the activities of GnRH and the information processing mechanisms of the nervous systems in higher animals. It can also serve as a base compound in the development of pesticides and drugs.The peptide has the GnRH activity and has the following amino acid sequence (I):