Melanin-concentrating hormone (MCH) is a cyclic, 19 amino acid peptide produced in the lateral hypothalamus and other regions of the mammalian brain. When administered intracerebrally or overexpressed transgenically in rodents, MCH stimulates food intake and weight gain. Two G protein-coupled receptors for MCH, MCHR1 and MCHR2, have been identified in humans, although rodents appear only to have MCHR1. Both MCHR1 and MCHR2 are expressed primarily in brain. MCHR1 has been demonstrated by genetic and pharmacological methods in rodent models to mediate obesity caused by a high fat diet or leptin deficiency. However, MCHR2 might play a similar role in the species that express it.