The expression of gangliosides of ganglio-series as well as neolacto-series gangliosides in anencephalic and in normal human fetal brain was compared with that in adult brain by immunostaining on thin-layer chromatograms. A difference in the expression of ganglio-series gangliosides with GM1a core was found between anencephalic and normal fetal brain, with less expression of GM1a and GD1a in anencephaly compared with normal fetal brain, in which these gangliosides dominate. Small amounts of GM1b were detected in fetal brain whereas only traces were found in anencephalic brain. Lactosamine-containing gangliosides were present in fetal and in anencephalic brain as alpha 2-3 as well as alpha 2-6 sialylated nLcOse4Cer structures. A heterogeneous group of neolacto-series gangliosides was expressed in anencephalic brain in both the monosialo- and presumed disialoganglioside range. These findings demonstrate a significant change in ganglioside pattern in anencephaly where the process of cell differentiation and maturation has been severely disturbed.