Content and composition of gangliosides were studied in brain white and grey substances of patients with mongolism. Content of gangliosides, which are typical components of plasmatic membranes of nervous cells, was decreased in brain grey substance of the patients as compared with control group, whereas content of the lipids was increased in white substance. Differentiation of neurones appears to be inhibited in mongolism. Content of disialoganglioside GDIa exceeded the content of other gangliosides in brain white and grey substances in normal state; content of GMI, GTI, GDIb was also increased. Composition of gangliosides from brain of the patients with not distinctly altered as compared with that of children of control group.