Magnetic search-coil oculography of three brothers, aged 20, 22, and 25, with Pelizaeus-Merzbacher disease (PMD) was used to demonstrate nystagmus not obvious on inspection at the W. K. Kellogg Eye Center, University of Michigan, Ann Arbor, MI. The method disclosed the presence of binocular elliptical pendular nystagmus in two patients and upbeat nystagmus in all three patients. This combination of elliptical pendular and upbeat nystagmus is not described in any other childhood neurodegenerative disease. In conjunction with MRI findings and supportive clinical signs a diagnosis of PMD is strongly indicated. 
COMMENT. PMD may be classified by age of onset into a classical infantile type, congenital type, and adult onset type. The classical and congenital forms have X-linked recessive inheritance whereas the adult onset type is autosomal dominant in inheritance. Nystagmus and head tremor are the first signs followed by spasticity, ataxia, choreoathetosis, optic atrophy, and dementia. PMD must be differentiated from congenital nystagmus or spasmus nutans, metachromatic leukodystrophy, adrenoleukodystrophy, Krabbe’s disease, and Cockayne’s syndrome. The MRI in PMD shows brain atrophy, increased T2 signal in white matter, and decreased signal in basal ganglia and thalami. Pathological correlations of upbeat nystagmus have shown dysmyelination of the pontomedullary tegmentum.