BACKGROUND: Previous imaging studies have demonstrated that schizophrenia is associated with increased striatal amphetamine-induced dopamine release, overwhelmingly evident in the exacerbation phase of the disease. Schizotypal personality disorder (SPD) is a schizotypal spectrum disorder genetically related to schizophrenia. The aim of this study was to investigate striatal dopamine (DA) function in patients with SPD. METHODS: Thirteen patients with SPD and 13 matched healthy controls were scanned using single photon emission computed tomography (SPECT) during a large pill (bolus) plus continuous D2/3 radiation tracer [123I] iodobenzamide (IBZM) infusion. Striatal specific to nonspecific equilibrium partition coefficient (V3″) was determined at baseline and at subsequent administration of amphetamine (0.3 mg/kg). RESULTS: No significant differences were seen between groups at baseline V3″. amphetamine-induced [123I]IBZM V3″ was reduced more in SPD patients (-12 ± 5%) than in controls (-7 ± 5%) (p = .03). CONCLUSION: Amphetamine-induced [123I]IBZM V3″ reduction in patients with SPD was similar to the outcome in patients with schizophrenia who were recovered (committed) (-10 ± 9%, n = 17) but significantly lower than the outcome in patients with severe disease (-24 ± 13%, n = 17). This suggests that DA dysregulation in schizophrenia spectrum disorders may have a trait component, seen in patients with recovered schizophrenia and SPD, and a state component, associated with exacerbation of psychosis but not with SPD.