Human glutamate receptor 4 (GRIA4) is a new member of the family of ionotropic glutamate receptors which are the predominant excitatory neurotransmitter receptors in the mammalian brain. Binding studies showed that human GRIA4 transfected into simian kidney cells (COS-1) exhibits high specific binding for[3H](RS)-alpha-amino- 3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA) but not [3H]kainate. Ion substitution experiments indicate that hGluR4 receptor-linked ion channels in their homomeric state are permeable to both CA2+ and Na+ ions. Immunoprecipitation studies suggest that GRIA1 exists in situ in the form of a pentamer.