Auditory brainstem responses (ABRs) were examined in six patients with autonomic failure with Parkinson's disease (AF with PD) and 10 patients with autonomic failure with multiple system atrophy (AF with MSA), all of which showed marked parkinsonian features as a principal sign. We designated the central abnormalities of ABRs as prolongation of latencies (wave III or V) and interpeak latencies (IPLs; I-III, I-V, and III-V IPL) or decreased amplitude ratios of wave III or V to those of wave I (less than 1.0). None of the patients with AF with PD showed abnormalities in ABRs. In contrast, in those with AF with MSA, the peak latencies or IPLs were prolonged in two of the 10 patients, and the amplitude ratios of wave III or V to those of wave I were decreased in other two of these patients. Moreover, both prolongation of latencies and a decreased ratio were observed in other one. Overall, five of the 10 patients with AF with MSA showed central abnormalities in ABRs. It is clinically difficult to differentiate AF with PD from AF with MSA, particularly when no cerebellar signs are apparent in AF with MSA patients. When central abnormalities of ABRs are observed in AF patients, AF with MSA should be suspected rather than AF with PD. In conclusion, ABRs provide useful information for the differential diagnosis of AF with PD and AF with MSA.