Gangliosides are normal cell surface components of all animal cells. Altered ganglioside biosynthesis during malignant transformation results in expression of a qualitatively and quantitatively different ganglioside profile in many tumors. While their physiological function is largely unclear, gangliosides expressed by cancer cells, e.g. GD3, GD2 and GM2 in malignant melanoma, have proven to be suitable targets for passive immunotherapy with monoclonal antibodies and for active immunotherapy with vaccines. Studies aimed at further augmenting the effectiveness of these approaches are currently underway.