We studied the nigrostriatal dopaminergic pathway in 3 patients with Shy-Drager syndrome, by using positron emission tomography and [18F]6-fluoro-1-dopa to determine whether their parkinsonism correlated with impaired functional integrity of the presynaptic nigrostriatal pathway. One patient had short duration of disease, mild parkinsonism, and a normal positron emission tomographic scan, suggesting pathological changes functionally distal to the nigrostriatal pathway. Two patients with longer duration of disease had more severe parkinsonism and reduced [18F]6-fluoro-1-dopa uptake, suggesting impaired nigrostriatal dopaminergic function with progression of Shy-Drager syndrome.