Striatonigral degeneration (SND) is difficult to diagnose in vivo. The purpose of this study was to detect the best indicators for an early and reliable diagnosis of the disease. Eighteen patients clinically diagnosed as having SND were selected with rigorous inclusion criteria and compared to 18 patients with Parkinson's disease (PD) matched for age and disease duration. Apart from dysautonomia, the principal discriminant clinical features that distinguished SND from PD were the early appearance of the following symptoms and signs: (a) severe and atypical progressive parkinsonism characterized by bilateral bradykinesia and rigidity, slowness of gait, postural instability, and falls, and poor or absent response to adequate levodopa treatment; (b) increased tendon reflexes associated or not with frank pyramidal signs, severe dysarthria, and less consistently, dysphagia, stridor, antecollis, and stimulus-sensitive myoclonus, which, when present, are highly suggestive of the disease.