Galactocerebrosides and sulfatides are major characteristic components of vertebrate myelin. In contrast, glucocerebroside is the major glycosphingolipid of shrimp nerve. In this study, the concentrations of these glycosphingolipids in the nervous systems of animals from several evolutionary branches were determined by use of high-performance liquid chromatography. In nerves of protostome animals only glucose-containing glycosphingolipids were detected, whereas glycosphingolipids from deuterostomes contained predominantly galactose. Neither the glycolipids containing alpha-hydroxy fatty acids nor sulfate esters of the glycolipids, both of which always accompany galactocerebrosides in deuterostome myelin, were present in protostome nerves. This correlation suggests an evolutionary trend from gluco- to galactocerebrosides, which corresponds with changes in the nervous system from loosely structured membrane-enwrapped axons to multilamellar highly structured myelin.