The lipid membrane composition of cerebral tissue from 5 patients with classic Rett syndrome, ages 12-30 years, and from 14 age-matched controls was studied. The results demonstrated a selective loss of myelin-associated lipids and an enrichment of gangliosides in temporal white matter. The ganglioside pattern revealed an increase of astroglial cell-associated gangliosides and reduced proportions of gangliosides GD1a and GT1b. This latter finding may be crucial in synaptic function. The fatty acid compositions of ethanolamine phosphoglyceride, choline phosphoglyceride, and galactosylceramide were normal.