We report the synthesis, binding properties and intrinsic activity at MT 1 and MT 2 melatonin receptors of new dimeric melatonin receptor ligands in which two units of the monomeric agonist N-{2-[(3-methoxyphenyl)methylamino]ethyl}acetamide (1) are linked together through different anchor points. Dimerization of compound 1 through the methoxy substituent leads to a substantial improvement in selectivity for the MT 1 receptor, and to a partial agonist behavior. Compound 3a, with a trimethylene linker, was the most selective for the MT 1 subtype (112-fold selectivity) and compound 3d, characterized by a hexamethylene spacer, had the highest MT 1 binding affinity (pK iMT1 =8.47) and 54-fold MT 1 -selectivity. Dimerization through the aniline nitrogen of 1 abolished MT 1 selectivity, leading to compounds with either a full agonist or an antagonist behavior depending on the nature of the linker.