The distribution of cerebral blood flow and metabolism is related to neuronal activity. Cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), and oxygen extraction fraction (OEF) in ten patients with Parkinson's disease and five age-matched normal control subjects were measured with positron emission tomography (PET) using 15O2, C15O2 steady state inhalational technique to investigate functional changes of the cortex and the basal ganglia in Parkinson's disease. All patients had no history of cerebrovascular disease and CT scan showed no abnormal findings except for moderate cerebral atrophy in only one patient. When the level of clinical disability was related on the scale of Hoehn and Yahr, one patient was stage I, four were stage II, four were stage III, and one was stage IV. Psychic symptoms which include hallucination, depression, and dementia were recognized in four patients. One of these four patients was mildly demented. Four patients were newly diagnosed and had never been treated with antiparkinsonian medication before. Before the patients had their PET study their antiparkinsonian medication was discontinued for more than three days. But in two patients PET study was performed without discontinuity of antiparkinsonian medication. The values for regional CBF and regional CMRO2 were lower in the patients than in the normal control subjects, especially in the frontal cortex there was a significant decrease of CBF and CMRO2. There was no discrepancy between CBF and CMRO2 both in the patients and the normal control. CBF and CMRO2 in the cortex and the basal ganglia were not correlated with the severity of tremor, bradykinesia, and rigidity.(ABSTRACT TRUNCATED AT 250 WORDS)