In order to analyse the relevance of the indole electronic region in the binding of melatonin to its receptors, we prepared several analogues with p-H, p-NO(2), p-MeO, p-F and p-Me of benzyl, benzoyl and phenyl substituents at position 1 of the melatonin skeleton. The electronic properties of the analogues, as calculated with the semiempirical method AM1, were correlated with their affinity for the melatonin receptor from chicken brain membranes. Different trends were observed for each compound series. Compound 5c, with a p-NO(2)-benzoyl group, showed the best affinity indicating the importance of a polar bulky group in the receptor interaction.