In starfish, the peptide hormone gonad-stimulating substance (GSS) secreted from nervous tissue stimulates oocyte maturation to induce 1-methyladenine (1-MeAde) production by ovarian follicle cells. Recently, GSS was purified from radial nerves of the starfish Asterina pectinifera and identified as a relaxin-like peptide. This study examines the mechanism of GSS secretion from radial nerves. When radial nerves isolated from A. pectinifera were incubated in artificial seawater containing ionomycin as a calcium ionophore, GSS release increased in a dose-dependent manner; 50% activity of GSS release was obtained with approximately 10 µM ionomycin. Another calcium ionophore, A23187, also stimulated GSS release from radial nerves. In contrast, membrane permeable cyclic AMP and cyclic GMP analogs failed to induce GSS release. These results suggest that GSS secretion is induced by intracellular Ca² as a second messenger.