The biologically active ganglioside molecular species, LG-2, which has been obtained from the starfish Astropecten latespinosus, was completely methylated followed by separation using reversed phase HPLC to give a methylated major component, LG-2M-5, in the pure state. The ceramide moiety of LG-2M-5 was indicated by the positive ion fast atom bombardment tandem mass spectrometry (FABMS/MS) of LG-2M-5. This fact was verified from the measurements of the positive ion FABMS/MS of the permethylates prepared from four known starfish cerebrosides.