D-Amino acid oxidase inhibitor is an inhibitor of D-amino acid oxidase (DAAO) with IC50 values of 145 and 114 nM in CHO cells expressing human and rat DAAO, respectively. It is selective for DAAO over a panel of 150 enzymes, receptors, and ion channels when used at a concentration of 30 μM. D-Amino acid oxidase inhibitor (10-200 mg/kg, i.p.) inhibits DAAO activity in rat kidney and cerebellum in a dose- and time-dependent manner. It increases levels of D-serine in rat plasma and cerebral spinal fluid (CSF) but has no effect on hyperlocomotion or dopamine efflux in the nucleus accumbens induced by amphetamine in rats. DAAO inhibitor reduces formalin-induced paw flinching in rats (EC50 = 0.17 μg per animal) indicating an antinociceptive effect.