2-Iodomelatonin is a potent agonist of melatonin receptor 1 (MT1) with a Ki value of 28 pM, exhibiting over 5-fold selectivity for MT1 compared to MT2. It can be used to identify, characterize, and localize melatonin binding sites in the brain and peripheral tissues.

6-Chloromelatonin is a potent melatonin receptor agonist, a 5-methoxyindole compound that competes for presynaptic melatonin receptor sites in the rabbit retina, inhibiting the calcium-dependent release of [3H]dopamine with higher metabolic stability than melatonin. Chloromelatonin competitively binds to [3H]melatonin at MT2 receptors (pKi=9.77) and may be used to study insomnia and sleep disorders associated with depression.

Luzindole (N-0774) is a selective melatonin receptor antagonist that inhibits experimental autoimmune encephalomyelitis and exhibits antidepressant-like activity. It preferentially targets MT2 (Mel1b) over MT1 (Mel1a), with Ki values of 10.2 nM for human MT2 and 158 nM for MT1.

ACH-000143 have been identified as a novel agonist of the melatonin receptors MT1 and MT2.

N-ACETYLTRYPTAMINE is a partial agonist for melatonin receptors in the retina. Also used for determination of serotonin N-acetyl transferase.

4-P-PDOT (4-phenyl-2- propionamidotetralin) is a potent, selective and affinity Melatonin receptor (MT2) antagonist.

UCM 608 (2-Phenylmelatonin) is an antagonist of melatonin-induced contractile responses at low concentrations and induces an increase in GDP-GTP exchange.