Human LGR8, initially discovered as a low-affinity relaxin receptor, has now been characterized as the INSL3 receptor. To investigate LGR8 function in the rat, an LGR8 ortholog was identified in the rat genome, and the full-length sequence was cloned and expressed. Rat LGR8 bound INSL3 with high affinity, clearly demonstrating that it is the rat INSL3 receptor. Interestingly, native rat relaxin did not activate rat LGR8, indicating that relaxin is not an endogenous ligand for rat LGR8. LGR8 mRNA expression was demonstrated in the gubernaculum at the time of testis descent and in the testis associated with germ cells.