Under physiological condition, NOS is the predominant pathway, as it has an ~1000-fold greater affinity for l-arginine than arginase,10 and endogenous agmatine levels in the mammalian brain are low.63 We found that l-arginine was close to l-citrulline in the control group; however, it became closer to agmatine in the schizophrenia group, indicating an altered relationship between l-arginine and its three main metabolites in schizophrenic brains. Here, NOS2 is linked to schizophrenia.