Abstract: PET and SPECT provide the means to studying in vivo the neurochemical, hemodynamic or metabolic consequences of the degeneration of the nigrostriatal dopaminergic system in Parkinson's disease (PD). Activation studies using cerebral blood flow and metabolism measurements during a motor task reveal an impaired ability to activate the supplementary motor area and dorsolateral prefrontal cortex in PD. The extent of striatal dopaminergic denervation can be quantified with PET and SPECT. Striatal uptake of ¹⁸F-dopa is markedly decreased in PD, more in the putamen than in the caudate nucleus, and inversely correlates with the severity of motor signs and with duration of disease. PET and SPECT make possible the assessment by noninvasive means of the changes in dopamine receptor density. Meanwhile, MRS can reveal changes in concentra-tion of several hydrogenate and phosphoric compounds in the brain. The functional information of brain in PD can be obtained with these complementary techniques.