Preliminary study on the receptor of gonad-stimulating substance (GSS) as a gonadotropin of starfish. Previously, the gonad-stimulating substance (GSS) which acts as the gonadotropin was purified from the starfish (Asterina pectinifera) and subsequently, its structure was deciphered. In this study, artificial GSS was synthesized and its interaction with the receptors was examined further. According to competitive experiments using radioiodinated and radioinert GSS in various tissues of A. pectinifera, high specific bindings were observed in the ovarian follicle cells and testicular interstitial cells. Scatchard plot analysis also showed that K(d) values were about 4nM in follicle cells and about 7nM in interstitial cells. The numbers of binding sites in follicle cells were estimated to be about 3pmoles/mg protein and in interstitial cells to be about 1pmoles/mg protein. These strongly suggest that GSS receptors are distributed to follicle cells in female and interstitial cells in male, respectively.