Human immunodeficiency virus type 1 (HIV-1) infection is associated with psychiatric complications including cognitive impairment, affective disorders, and psychosis. Previous studies have revealed a disturbed kynurenine metabolism in these patients leading to increased levels of neuroactive compounds acting at glutamatergic neurotransmission. Kynurenic acid (KYNA), one of these metabolites is a glutamate-receptor antagonist, preferentially blocking the glycine site of the N-methyl-d-aspartate (NMDA) receptor. Increased levels of brain KYNA have been suggested to induce a NMDA receptor hypofunction that is associated with psychotic symptoms. In the present study, we analyze the concentration of KYNA in the cerebrospinal fluid (CSF) from HIV-1 infected patients (n=22), including HIV-1 infected patients with psychotic symptoms (n=8) and HIV-1 infected patients without psychiatric symptoms (n=14). We found that HIV-1 infected patients had significantly higher median concentration of CSF KYNA (3.02nM) compared to healthy controls (1.17nM). Furthermore, CSF KYNA levels were significantly elevated in HIV-1 infected patients with psychotic symptoms (4.54nM) compared to patients with HIV-1 without psychiatric symptoms (2.28nM). Present results indicate that increased levels of CSF KYNA may be associated with development of psychotic symptoms in HIV-1 infected patients.