A series of glycinamides, derivatives of diphenyl imidazolon-4-one was designed and obtained as potential ligands of the glycine binding site of NMDA receptors. The compounds were evaluated in vitro for their affinity for the glycine binding site of NMDA receptors using [3H]-L-689,560 as radioligand. Their anticonvulsant activity was estimated in vivo in a maximal electroshock seizure (MES) and subcutaneous pentylenetetrazole (scMet) tests. The volume and the surface of the molecules seem to be important in elucidating the relation between the structure and the pharmacological properties.