Binding of [3H](2S,4R)-4-methylglutamate, a novel low affinity kainate receptor agonist, was studied in brain sections of a Macaca fascicularis monkey. In cerebellar sections, [3H](2S,4R)-4-methylglutamate bound to a single population of sites (KD = 20 nM) and was inhibited by various glutamate receptor ligands: kainate > 6-cyano-7-nitroquinoxaline-2,3-dione > L-glutamate >> AMPA. (S)-5-lodowillardiine and (RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl)propanoic acid (ATPA), drugs selective for the GluR5 subunit, displaced 50% and 40% of binding, respectively. Autoradiography revealed topographic binding of [3H](2S,4R)-4-methylglutamate. Binding in cortex was highest in layer 5 and restricted to CA2/3 in hippocampus. Levels of binding were high in septum and hypothalamus. Moderate densities of binding were found in caudate-putamen, cerebellar granular layer, nucleus tractus solitarius, cuneate nucleus and area postrema. Binding in spinal cord was concentrated in dorsal horn. [3H](2S,4R)-4-Methylglutamate shows differential binding throughout primate brain and is a valuable new ligand for low affinity kainate receptors.