The present invention relates to a mammalian melanocortin receptor. The invention is directed toward the isolation, characterization and pharmacological use of a mammalian melanocortin receptor (MC3-R). The invention specifically provides a particular melanocortin receptor, termed MC3-R, isolated as a complementary DNA copy of mRNA corresponding to the gene for this receptor in rats. Also provided is a eukaryotic recombinant expression construct capable of expressing a mammalian melanocortin receptor in cultures of transformed eukaryotic cells and such cultures of transformed eukaryotic cells that synthesize a mammalian melanocortin receptor. The invention also provides methods for screening in vitro agonists and antagonists of such a melanocortin receptor using preparations of receptor protein from such cultures of eukaryotic cells transformed with a recombinant expression construct.