An analogue of human melanin-concentrating hormone (MCH) suitable for radioiodination was designed in which Tyr13 was replaced by Phe and Val19 by Tyr. The resulting monoiodinated [125I] [Phe13,Tyr19]-MCH radioligand was biologically active and led to the discovery of high-affinity binding sites on mouse B16-F1, G4F and G4F-7 melanoma cells. Saturation binding analysis with G4F-7 cells revealed 1090 MCH receptors per cell and a KD of 1.18 x 10(-10) mol/l. Receptors for MCH were also found on rat PC12 phaeochromocytoma cells, human RE melanoma cells and COS-7 cells. Competition binding analyses with other peptides such as alpha-MSH, NPY and PACAP demonstrated that MCH receptor binding is specific. rANF(1-28) was found to be a weak competitor of MCH, indicating topological similarities between MCH and rANF(1-28) when interacting with MCH receptors.