Sphingolipids participate in fundamental biological processes, such as cell-cell interaction, proliferation, differentiation, oncogenic transformation, immune recognition and responsiveness, and serve as receptors for microbial membrane lectins and viral and bacterial toxins (see Refs 1 and 2 for reviews). It has been known for some time that sphingolipids (especially those with carbohydrate moieties) undergo dramatic alterations in both structure and membrane organization during oncogenic transformation, suggesting a role for these molecules in the regulation of cell growth and differentiation. Subsequently, the identification of sphingolipids as bloodgroup antigens, stage-dependent embryogenic antigens, and tumor antigens has greatly increased interest in these molecules as mediators of cell-cell interactions. On the basis of observations such as these, research into the mechanism (s) of sphingolipid action focused primarily on their ability to function as mutable structural components of the cell membrane and as' primitive'cell surface receptors. Now attention is being drawn towards the role of sphingolipids as intracellular signal transduction mediators and, as a result of increased study, many novel functions for sphingolipids are being identified.