We should like to subsume under the group designation “mucolipide” the complex lipide polymers that combine constituents commonly considered characteristic of the cerebrosides with others usually assigned to the mucoids. They are soluble in water, but also in organic solvents, and they contain fatty acid, a sphingosine-like base, a hexose, also amino sugar, sometimes amino acids, and, most significantly, sialic acid or a related substance. This has been pointed out recently in notes dealing briefly with the subject of this communication (1, 2).’ Lipides of the general type under discussion here, i.e. compounds related to the cerebrosides, but soluble in water and yielding a violet color with Bial’s reagent or a direct color reaction with p-dimethylaminobenzaldehyde without previous treatment with alkali, have been encountered not infrequently in the older literature. Since what appears to be their first description, by Landsteiner and Levene (4, 5), similar substances were found in spleen (6), normal brain (7), and in the brain of cases of NiemannPick disease (8) and of Tay-Sachs disease (9). Two representatives of the mucolipide group have been investigated in some detail. (1) The “gangliosides,” a name first given to mucolipides isolated from brain tissue of instances of lipidoses (10) and later extended, perhaps without justification, to material from normal nervous and other tissues; and (2) “strandin,” a high molecular lipide complex from ox brain (11). Folch and his collaborators (11) deserve great credit for pointing out the existence in nervous tissue of a lipide derivative of high molecular weight. For the isolation of this material, they employed a much milder procedure than is customary