New solvent systems consisting of acetonitrile, isopropanol and aqueous 50 mM potassium chloride or 2.5 M ammonium hydroxide were developed for the separation of gangliosides by high-performance thin-layer chromatography. These solvent systems seem to be superior for the resolution of polysialogangliosides such as tetra-, penta- and hexasialo species, as compared to chloroform-methanol-aqueous salt systems. The order of mobility of gangliosides in the ammoniacal solvent system is GD3 greater than GD1a greater than GM1 greater than GT1b greater than GD1b as compared with GM1 greater than GD3, GD1a greater than GD1b greater than GT1b in the neutral septem. A combination of these two solvent systems provides excellent two-dimensional separations of complex ganglioside mixtures. The neutral solvent system, acetonitrile-isopropanol-aqueous 50 mM potassium chloride, can be used for the separation of underivatized gangliosides by high-performance liquid chromatography on an Aquasil SS silica gel column. Ganglioside elution can be monitored at 208 nm because of the good UV-transparency of the effluent.