Accumulating evidence implicates kynurenic acid, a modulator of glutamatergic and cholinergic neurotransmission, in the pathophysiology of schizophrenia and bipolar disorder. These neuropsychiatric disorders are associated with increased kynurenic acid within the brain and reduced expression of kynurenine 3-monooxygenase (KMO), which indirectly regulates kynurenic acid levels. To investigate the neurobiological mechanism by which genetic KMO deficiency contributes psychosis-like behavior, we generated mice with a targeted deletion of the KMO gene. Kynurenine and kynurenic acid levels were markedly increased in both plasma and brain of KMO−/− mice compared to wild type (WT) control mice. As a behavioral correlate for positive symptoms of schizophrenia, we examined amphetamine-induced locomotor which is significantly enhanced in KMO−/− mice relative to controls. This is correlated with an increase in amphetamine evoked dopamine efflux in the nucleus accumbens, as determined by in vivo microdialysis. To better understand the potential mechanisms underlying this effect, we performed in vivo chronoamperometry to measure the rates of dopamine clearance. Amphetamine-evoked dopamine clearance was significantly reduced in KMO−/− mice compared to WT. Together, these data identify aberrant DAT function in KMO−/− mice as a likely mechanism driving psychosis-like behavior.