Brain grey and white matter of a case of Pelizaeus‐Merzbacher disease (connatal type Seitelberger) of a 19‐month‐old boy were analysed with respect to lipids. Cerebrosides and sulfatides were totally absent in the pathological brain. In comparison to control, differences in gangliosides could be detected in grey and white manner. C18:1, fatty acids were markedly reduced in the main glycerophospholipids of white matter. In sphingomyelin of cortex and white matter 90% of fatty acids were C18:0; longer chains were absent. In contrast: PNS (nervus fernoralis) lipids contained the main galactolipids. However, these a s well as all other lipid classes showed a 20% reduction compared with values obtained from nervus femoralis of an infant of the same age. The fatty acid patterns of all lipid classes were determined. The only marked deviations from normal were observed in the C24‐chains of cere‐brosides and sulfatides. The formalin‐fixed brain of an older brother (same disease) was analysed only with respect to glycolipids: neither cerebrosides nor sulfatides could be detected.