A point mutation within the coding sequence of the primary subunit of the N-methyl-d-aspartatge (NMDA) subtypr of glutamate receptor (glutamine substitution for histidine at position 780) exhibits a higher affinity for NMDA than the wild type receptor (EC50 5 versus 27 μM). To our knowledge this is the first point mutation of this ligand-gated ion channel described with higher agonist affinity. This observation may help further localize the agonist binding site and help to understand the heterogeneity of agonist affinity within the glutamate receptor family.