Melanin-concentrating hormone (MCH) is a hypothalamic orexigenic peptide. Recently, an orphan G-protein-coupled receptor (SLC-1) was identified that binds RICH with high affinity. Here, we demonstrate the mRNA expression of this receptor in insulin-producing cells Including CRI-G1 and RINm5F cells, and in rat islets of Langerhans. Immunofluorescence studies in CRI-G1 and RINm5F cell-lines demonstrated cell-surface expression of the receptor. Rat MCH significantly stimulated insulin secretion in both cell-lines, The potency and the efficacy of RICH were significantly increased in the simultaneous presence of forskolin, suggesting that MCH may amplify the insulinotropic effect of cyclic AMP elevating stimuli. Salmon RICH, which differs from rat/human MCH by six amino acids, was less efficacious than rat/human RICH in stimulating insulin release. The data provide evidence for the expression of MCH receptors in insulin producing cells. The insulinotropic effect of RICH may contribute to the regulation of metabolism and energy balance by this peptide,