Nine positron emission tomography studies of regional cerebral glucose metabolism were performed in 7 patients with probable striatonigral degeneration, a disorder characterized by parkinsonian features and absent or poor response to L-dopa. When compared with values obtained in normal volunteers, mean cerebral glucose metabolism was slightly reduced in subjects with striatonigral degeneration who, in addition, had a marked (20.5%, +/- 3 SD) relative hypometabolism in putaminal and caudate nuclei. Significant hypometabolism was also found in motor/premotor as well as in prefrontal cortex. In 2 subjects who were studied twice a deterioration of relative striatal metabolism paralleled clinical evolution. Magnetic resonance imaging disclosed the presence of abnormal iron deposits in the putamen in all cases but showed no cortical anomalies. These results suggest that positron emission tomography with [18F]fluorodeoxyglucose may provide an index of cell and processes degeneration in the striatum in striatonigral degeneration and is able to detect functional deficits in frontal cortex. The presence of striatal hypometabolism might be a predictor of a poor response to L-dopa.