agonists and antagonists of 5-HT4receptors, were synthesized. They were evaluated using radioligand binding assays with [3H]GR 113808, a 5-HT4receptor selective ligand, in the rat striatum and the electrically stimulated myenteric plexus longitudinal muscle of the guinea pig. In contrast to the previously described ester derivatives, a drop in the affinity for 5-HT4receptors was observed and the compounds