The major phospholipid classes of the human red blood cell membrane are: phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and sphingomyeli. These phospholipids are distributed asymmetrically across the two halves of the lipid bilayer. this asymmetry appears to be generated and maintained by an ATP-dependent translocation of aminophospholipids from outer to inner leaflet, and by the interaction of phospholipids with skeletal proteins. The phosphoinositides account for 3-4% of total erythrocyte membrane phospholipid. They play an important role in signal transduction and are involved in other various membrane functions.