For decades the way of viewing of the cell membrane has changed considerably. At the beginning of the twentieth century the cell membrane was visualized as a lipid bilayer. Following researches have discovered that the cell membrane contains also proteins. In 1972 Singer and Nicolson introduced the division of membrane proteins into peripheral and integral proteins. Singer and Nicolson had also conduc-ted research on cells fusion, which have laid the foundation of the membrane model as a fluid mosaic of lipids and proteins. The Singer and Nicolson model in many aspects is still valid.

In this paper the current opinions on the structure and function of the lipid rafts heterogeneous, sterols and sphingolipids rich microdomains that occur in the plasma membrane but also in the membranes of some intracellular organelles e.g. Golgi complex, endoplasmic reticulum or mitochondria were presented. Lipid rafts have different dimensions. Their diameters often range from 50 to 100 nm, but larger forms with diameters of 200500 nm also exist. The smallest lipid raft with diameter of 5 nm lipid raft contains approximately 3040 lipids and 610 characteristic proteins.

The classical bilayer model of cell membrane structure proposed by Singer and Nicholson in 1972 has recently been modified. Research has shown that lipid molecules in the membrane do not have a random horizontal distribution but form submicroscopic domain enriched in cholesterol, sphin- golipids and gangliosides. These lipid microdomain (also named lipid rafts) have been visualised in living cells by a variety of methods including fluorescence microscopy with lipid-specific probes, scanning probe microscopy and cryoelectron microscopy.