Brainstem auditory evoked responses (BAERs) were recorded in seven patients with Pelizaeus-Merzbacher leukodystrophy (PMD), two with adrenoleukodystrophy (ALD), and one with metachromatic leukodys-trophy (MLD). BAERs were altered in all patients, and the alterations were severe in 9 of the 10 patients. A patient with ALD who as yet had no neurologic symptoms showed only minimal abnormality of the BAERs, consisting of prolongation of the latency of wave V. In the remaining nine patients, only wave I generated in the extramedullary portion of the eighth nerve was recorded with or without a wave II. Subsequent components (III through VII) were absent. No abnormality of BAERs was observed in the 10 known carriers of PMD. The combination of BAERs and EEG is helpful in differentiating leukodystrophy from progressive gray matter diseases.