Abstract A variety of naturally occurring and synthetic analogues of the putative excitatory amino acid neurotransmittersl-glutamic acid (l-GLU) andl-aspartec acid (l-ASP) are powerful neuroexcitatory and neurotoxic agents. These effects appear to be mediated primarily by the central receptors normally operated byl-GLU and/orl-ASP. Administration of some of these amino acid analogues to animals provokes symptoms and neuronal alterations similar to those observed in patients suffering from epilepsy and Huntington's chorea. These observations have brought the central receptors forl-GLU and/orl-ASP into focus as potential pharmacological sites of attack. Some heterocyclic amino acid excitants including AMPA, an analogue of the mushroom constituent ibotenic acid, have proved to be useful tools for characterization of the excitatory amino acid receptors. These aspects and recent comparative pharmacological studies using different radioactive ligands, including [ 3 H]AMPA, will be discussed.