This unit describes a competitive binding assay for the glycine binding site on the NMDA subtype of glutamate receptors in rat brain homogenates. Agonists of the NMDA receptor associated glycine binding site have been proposed as potential therapeutics in cognitive disorders. Conversely, antagonists may be useful in a variety of disorders associated with excessive activation of EAA receptors, including Parkinson, Huntington and Alzheimer Diseases, and neuropathic pain, among others. This unit describes a competitive binding assay for the glycine binding site on the NMDA subtype of glutamate receptors in rat.