An isolated and purified GnRH protein receptor protein including an amino acid sequence selected from the group and an isolated and purified DNA which comprises a nucleotide sequence coding for the GnRH protein receptor protein. Also, a vector comprising the DNA of the GnRH protein receptor protein, a transformant carrying the vector comprising the DNA of the GnRH protein receptor protein, a process for producing a GnRH protein receptor protein or a salt thereof including culturing the transformant carrying the vector comprising the DNA of the GnRH protein receptor protein under sufficient conditions and for appropriate time to express the GnRH protein receptor protein, and a method of screening for a ligand to the GnRH protein receptor protein including contacting the GnRH protein receptor protein or a salt thereof with a sample to be tested. A screening method for a compound capable of inhibiting binding of the GnRH protein receptor protein with a ligand. Also, a kit for screening a compound capable of inhibiting binding of the GnRH protein receptor protein with a ligand including the GnRH protein receptor protein or a salt.