N-isopropyl-p-[[sup 123]I]iodoamphetamine (IMP) SPECT studies were performed on 21 patients (13 females; 45-73 yrs) with idiopathic Parkinson's disease (PD) and 10 age-matched normal controls (39-69 yrs). Regional cerebral blood flow (rCBF) was quantitatively measured by the arterial blood sampling method. When compared with normal controls, global CBF, and rCBF in the frontal cortex and in the basal ganglia were reduced 22.1% (p<0.01), 25.0% (p<0.05) and 25.6% (p<0.01), respectively. The reduction of rCBF in the basal ganglia was significantly correlated (p<0.05) with symptoms such as gait disturbance, frozen gait and motor disability score. However, no significant correlation was observed between the severity of dementia and any regional reduction of CBF, including the frontal or parietal cortices. These data show that the severity of dementia in PD may be related to other factors but not with CBF. Quantification of rCBF with [sup 123]I-IMP SPECT imaging is useful for evaluation and follow-up of patients with PD. (author).