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The functional integrity of striatal post-synaptic dopamine D2 receptors is requested for an effective pharmacologic treatment in patients with extrapyramidal movement disorders. Iodine-123 IBZM Single Photon Emission Computed Tomography (SPECT) is a noninvasive radionuclide technique for the morpho-functional imaging of post-synaptic dopamine D2 receptors. In this study, the results of iodine-123 IBZM SPECT and those of apomorphine tests were compared in 32 patients with extrapyramidal movement disorders--22 patients with idiopathic Parkinson's disease (IPD) and 10 with Parkinson's plus syndrome (PPS). Iodine-123 IBZM uptake was measured as the ratio between striatum and frontal cortex activities. Twenty of 22 IPD patients (91%) responded to apomorphine administration, while in 8 of 10 PPS patients (80%) the apomorphine test was negative. Iodine-123 IBZM uptake was significantly higher (p < 0.01) in IPD patients (1.39 +/- 0.114) than in PPS patients (1.27 +/- 0.078). Similarly, iodine-123 IBZM uptake was significantly higher (p < 0.01) in the patients with positive than in those with negative apomorphine test (1.38 +/- 0.113 vs. 1.26 +/- 0.078). In conclusion, the results of this study demonstrate that iodine-123 IBZM SPECT is a radionuclide technique capable of characterizing the patients with extrapyramidal movement disorders and of selecting the subjects who may respond to pharmacological dopamine treatment.