Studies have been made on gangliosides from various parts of the brain in 5 species of cartilaginous fishes, 2 species of teleosts, 2 amphibian species, 2 avian species and 3 species of mammals. Almost in all the species investigated, the highest content of gangliosides per weight unit of the brain were found in the forebrain (determinations were carried out by sialic acid, sometimes by sphingosine). Ganglioside content of brain structure in warm-blooded animals is higher that in corresponding structures of fishes and amphibia. Comparative studies on ganglioside composition in the brain of fishes and mammals indicate that brain structures exhibit the same pattern of molecular organization, as the whole brain of the species studied (high polysialoganglioside content in teleosts, predominance of gangliosides with a short carbon chain in cartilaginous fishes, etc.). Besides this fact, peculiarities of composition typical of the brain structures were found as well (more polar composition of gangliosides of the cerebellum and some other ones).