Single-strand conformational polymorphism analysis of an affected male with Pelizaeus-Merzbacher disease (PMD) showed a slight change in mobility of amplified exon 5 of the proteolipid protein (PLP) gene. The exon was sequenced and a G-->A transition at codon 216 was found. This mutation eliminates a BstNI restriction site and creates a MaeI restriction site. In 1989, Gencic et al. reported a mutation that destroyed the same BstNI site, but resulted in a substitution at codon 215 [Am J Hum Genet 45:435-442]. The mutation we report here is also present in the patient's mother and her male fetus as determined by polymerase chain reaction analysis of amniocytes.