The localization of major gangliosides in adult rat cerebellum was investigated by immunofluorescence technique with mouse monoclonal antibodies (MAbs). Five MAbs (GMB16, GMR17, GGR12, GMR5, and GMR13) that specifically recognize gangliosides GM1, GD1a, GD1b, GT1b, and GQ1b, respectively, were used. Our studies have revealed that the expression of the ganglioside is highly localized to a specific cell-type and layer in the rat cerebellum. GM1 was expressed in myelin and some glial cells. GD1a was detected exclusively in the molecular layer. GD1b and GQ1b were present restrictedly on the granular layer; GD1b was detected on the surface of the granular cell bodies, whereas GQ1b was present in the cerebellar glomerulus. GT1b was distributed intensely in both the molecular layer and the granular layer.