A new aspect of cell membrane structure is presented, based on the dynamic clustering of sphingolipids and cholesterol to form rafts that move within the fluid bilayer Simons lkonen, Nature 387(1997)569-572.A new aspect of cell membrane structure is presented, based on the dynamic clustering of sphingolipids and cholesterol to form rafts that move within the fluid bilayer. ------ Simons & Ikonen, Nature 387 (1997) 569-572