Brain function was measured in 5 patients with clinically diagnosed Steele-Richardson-Olszewski syndrome using positron emission tomography and tracers of dopamine metabolism, blood flow and oxygen metabolism. A global decrease in blood flow and oxygen utilization compared with normal values was found but the decrease was more marked in the frontal regions. The degree of impairment in oxygen utilization in the frontal region paralleled roughly the duration of the disease. Blood flow was impaired to a greater extent than oxygen utilization, resulting in raised oxygen extraction. This can partially be explained by a lower pCO2 in the patients. Alternatively it may imply involvement of brain vasculature in the pathophysiology of the disease in addition to neuronal degeneration. Striatal dopamine formation and storage, as indicated by L-(18F)fluorodopa uptake, was significantly decreased compared with control values. The severity of this decrease paralleled the degree of reduction in frontal cerebral blood flow. The results suggest that the impairment of cerebral function in Steele-Richardson-Olszewski syndrome is determined to a large extent by brainstem pathology.