The present study is the first to examine the modulation of retinal kynurenic acid (KYNA) content in response to N-methyl-D-aspartate (NMDA)-induced cell death in adult rat retinal ganglion cells (RGC). Adult Brown Norway rats were intravitreally injected with NMDA or PBS. Surviving RGC were retrogradely labeled with fluorogold and counted in wholemounts of retinas 2, 7 and 14 days after injection. Retinal KYNA content was measured by HPLC at the same time points. RGC numbers decreased significantly 2, 7 and 14 days after NMDA injection if compared to control retinas. KYNA concentration increased significantly two days after NMDA-injection. However, 7 and 14 days after injection retinal KYNA content was found markedly decreased in NMDA-treated eyes as compared to controls. It is conceivable that KYNA deficiency is causally related to the pathology of excitotoxic retinal diseases.